Results from FOCUS4-C

Scientific rationale for FOCUS4-C

The full report of the FOCUS4-C trial has been published.27 Parts of this chapter have been reproduced by Seligmann et al.27 This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 4.0) license, which permits others to distribute, remix, adapt and build upon this work, for commercial use, provided the original work is properly cited. See: https://creativecommons.org/licenses/by/4.0/. The text below includes minor additions and formatting changes to the original text.

The cellular DNA damage response (DDR) is mediated through complex pathways, which trigger the mobilisation of cell cycle checkpoints and DNA repair proteins to halt cell cycle progression. This allows the repair of damaged DNA prior to critical phases of replication or entry into mitosis, maintaining genomic stability. However, genome instability is considered an ‘enabling characteristic’ of cancer66 and a wide range of DDR genes are mutated in cancer cells.67

Targeting the DDR has been an effective therapeutic strategy in several tumour sites, including ovarian and pancreatic cancer.68,69 These agents can be used as monotherapy in cancers with defective DDR, where a ‘synthetic lethality’ interaction might be expected: two pathways together perform an essential function and the loss of one pathway (e.g. owing to mutation) is tolerated, but loss of both pathways leads to cell death.70

Wee1 is a nuclear tyrosine kinase that has a central role in cell cycle regulation, including being the key regulator of the G₂/M checkpoint through actions on CDK1, optimising DNA–histone stoichiometry prior to mitotic entry71 and modulating CDK1/2 during the intra-S-phase to block replication initiation.72 Inhibition of Wee1 causes unscheduled entry into mitosis, aberrant firing of replication origins leading to deoxyribonucleotide triphosphate shortage and replication stress, and accumulation of DNA damage during S-phase, which all lead to increased reliance on the G1/S checkpoint.71 Adavosertib is the first small molecule inhibitor of Wee1 kinase and has been tested in combination with chemotherapy and radiotherapy,73,74 but more recently as monotherapy to generate synthetic lethality in tumours with DDR defects.

In FOCUS4-C, adavosertib was tested in RAS- and TP53-mutant (RAS-/TP53-mutant) metastatic CRC, with the hypothesis that it would be sensitive to Wee1 inhibition. TP53 is a key regulator of the G₁/S checkpoint;75 loss of function leads to dependence on the intra-S and G₂/M checkpoints to detect DNA damage and initiate repair.76 In preclinical studies, adavosertib demonstrated preferential killing of TP53-deficient compared with TP53 wild-type tumours.77 Mutant RAS, as well as having recognised actions through downstream MAPK-AKT pathway signalling, also drives cell cycle progression, leading to replication stress during S-phase.78 In preclinical studies, mutant RAS was demonstrated to drive cells into S-phase through regulation of the CDK4 or CDK6 complex, and provides sustained mitogenic signals through sustained CDK2 activity. These effects activate the replication stress response, including checkpoint activation.79 Adavosertib plus mTOR inhibition in KRAS-mutant CRC was associated with inhibition of cell growth in in vitro models.80

Theoretically, a tumour with both TP53 loss and RAS mutation will be highly vulnerable to adavosertib: such a tumour will have G₁ checkpoint failure and evidence of replication stress and will be reliant on the intra-S-phase and G₂/M checkpoints. In a post-adavosertib treatment biopsy of a RAS-/TP53-mutant patient, the tumour had invoked both mechanisms of response to Wee1 inhibition, with evidence of DDR with Cdk2 activation and mitogenic signalling, compared with baseline.81 Therefore, it was hypothesised that the combination of these two mutations was likely to produce a more potent synthetically lethal interaction with adavosertib than either alone.

FOCUS4-C was designed to assess the safety and efficacy of adavosertib compared with active monitoring in patients with metastatic CRC whose tumours were RAS-mutant and TP53 mutant and have achieved disease stability following induction chemotherapy.

Study methods

Trial approvals, patient eligibility and recruitment

The trial and subsequent amendments were approved by the UK National Ethics Committee Oxford – panel C – and by the MHRA. Patients with newly diagnosed metastatic CRC were registered into the FOCUS4 trial programme from 88 UK hospitals. Patients were randomised into the FOCUS4-C trial in a subset of 25 hospitals between June 2017 and March 2020. Patients aged ≥ 18 years with newly diagnosed locally advanced or metastatic CRC were assessed for eligibility for FOCUS4-C if their tumour was confirmed to have both RAS and TP53 mutations (using NGS platform) and if they remained stable or responding after 16 weeks of first-line treatment. Patients were required to have a baseline randomisation CT scan performed within 4 weeks prior to randomisation; a minimum 3-week washout period after the last dose of chemotherapy or biological therapy and before the first dose of adavosertib; adequate renal (creatinine clearance greater than 50 ml/minute) and liver function; a WHO performance status of 0–2; and no evidence of prolonged QT interval on electrocardiogram.

Trial procedures

Adavosertib was supplied by AstraZeneca Ltd (Cambridge, UK). The packaging, labelling and distribution of adavosertib were undertaken by Fisher Services (Horsham, UK). Patients randomised to adavosertib continued to receive the drug until disease progression, death or intolerable toxicity. The first 21 patients received 250 mg of adavosertib once daily on days 1–5 and 8–12 of a 3-week cycle. The next 23 patients received 300 mg of adavosertib once daily on the same schedule. Patients took an oral 5-HT3 antagonist with each dose, and 4 mg of oral dexamethasone was given on days 1 and 8 of each cycle unless clinically contraindicated. Patients were asked to complete a diary card to record the day and number of pills taken.

Owing to the mandatory supportive medication for nausea and vomiting, for which a placebo was not available, blinding was not possible and active monitoring was used as the control arm. Patients randomised to active monitoring followed the same follow-up schedule and remained off any other anti-cancer treatment until clinical or radiological evidence of disease progression.

Patient tumour status was assessed every 8 weeks by CT scan, which was reviewed at the treating hospital site according to RECIST, version 1.1. Toxicities and symptoms were assessed locally every 4 weeks from randomisation or the start of treatment using the NCI common terminology criteria for adverse events (version 3.0). Patients were followed until progressive disease occurred, at which point the patient was recommended to restart first-line chemotherapy.

Treatment was stopped in the event of grade 3 or worse toxic effects or persistent toxicities judged to be medically significant or not tolerated by the patient, until the toxicity resolved to grade 1 or better.

Statistical methods

Treatment allocation

Patients were allocated to adavosertib or active monitoring using a 2 : 1 allocation ratio by minimisation with a random element of 20% by a centrally managed telephone service at the MRC CTU at UCL. Minimisation factors were as follows: treating hospital site, site of primary tumour [right colon (defined as proximal to and including splenic flexure), left colon or rectum], WHO performance status (0 or 1), 16-week CT scan result (stable disease, partial response or complete response), number of metastatic sites (none, one, or two or more) and first-line chemotherapy regimen.

Outcome measures

The primary outcome for FOCUS4-C was PFS, defined as the time from randomisation to either disease progression (according to RECIST criteria) or death from any cause. OS was a secondary outcome, defined as the time from randomisation to death from any cause. Other secondary outcomes included safety, toxicity and tumour response.

Sample size calculation

FOCUS4 used a MAMS design that allowed pre-planned signal-seeking analyses to inform a decision on whether or not to continue the trial. The nstage package under Stata version 14.1 was used to calculate the operating characteristics for each molecular trial. A median PFS of 3.6 months in the active monitoring arm was assumed based on a similar group of patients being followed up in the COIN trial.16 A target HR of 0.5 was sought for PFS, with a randomisation ratio of 2 : 1. Overall power was maintained at 80% at the one-sided 0.025 significance level, corrected for one closed interim and one final analysis. The recruitment target of 113 patients was based on the projected number of patients that we anticipated would be recruited when a target of 26 PFS events had occurred in the active monitoring arm. In addition, a prespecified interim analysis for futility was triggered when at least 13 PFS events had occurred in the active monitoring arm.

Statistical analysis

All analyses were carried out in accordance with a predefined SAP that was agreed before database lock and were undertaken using Stata version 16.1. Given that this was a Phase II efficacy signal-seeking study, the primary analysis was prespecified as the per-protocol analysis, which was defined as patients who had completed at least one cycle of trial treatment. Analyses were also carried out according to intention to treat (ITT). Patients were censored using the following criteria:

• For survival status, patients were censored on the date that they were last known to be alive, which was recorded as the latest of either the date of collection of a prescription from their hospital pharmacy or the date of a follow-up visit or CT scan.
• For PFS, patients were censored without progression on the date of the last CT scan showing no progression.
• For patients who died before a follow-up visit or CT scan, the date of death was used as the date of the event and assumed death without progression providing that the death occurred within 3 months of randomisation or any previous CT scan confirming no progression.

Kaplan–Meier curves were used to present survival data and Cox regression modelling was used to estimate HRs between randomised arms. Unadjusted HRs were estimated, as well as HRs adjusted for the stratification factors that were used to minimise patients into allocated groups (primary analysis). A further analysis also adjusted for resection status, timing of metastatic disease, alkaline phosphatase, white blood cell count, age of tumour sample and use of aspirin at baseline. Deviation from non-proportional hazards was assessed using regression of scaled Schoenfeld residuals against the log of time.

Tolerability, toxicity and safety reviews

Two tolerability assessments were undertaken by the IDMC, which made recommendations on (1) which sites were permitted to recruit patients into FOCUS4-C on the basis of their experience of unlicensed drugs and (2) whether or not a higher dose of medication may be tested. The trial commenced with a starting dose of 250 mg but with the possibility of this dose increasing to 300 mg if the lower dose was well-tolerated.

Exploratory analyses based on molecular profiles

The RAS cases were divided into two molecular subtypes: KRAS versus NRAS mutants, and KRAS codons 12 and 13 versus NRAS/KRAS mutants outside codons 12 and 13. TP53 mutations were divided based on the presence of missense or truncating mutations (including nonsense, frameshift and splice site mutations).

To understand the prognostic implications of mutation subtypes, mutation data from 438 patients from the S:CORT programme30 from the FOCUS trial82 were retrieved, which represented a similar clinical setting as FOCUS4-C. Tumours had been successfully sequenced (Illumina; San Diego, CA, USA) with a targeted panel (SureSelect; Agilent, Santa Clara, CA, USA). Among other genes, the panel spanned all coding exons of KRAS, NRAS, BRAF and TP53.83 Variant calling was performed with CaVEMan (Genome Research Ltd, Wellcome Trust Genome Campus, Saffron Walden, UK) for single-point mutations and Pindel (Genome Research Ltd) for insertions/deletions. Cases showing either MSI or BRAF mutation without MSI were grouped separately. The remaining cases were classified into four groups according to their combination of mutational status by RAS genes (KRAS/NRAS) and TP53. Kaplan–Meier plots and univariable survival analysis by Cox proportional hazard model were carried out according to the final six molecular subgroups.

Study results

Recruitment and patient characteristics

Between April 2017 and March 2020, 817 patients were registered into the FOCUS4 trial with successful biomarker profiling (Figure 4). A total of 247 patients (34%) had tumours confirmed to have both RAS and TP53 mutations (RAS/TP53 mutant). Of these patients, 151 had stable or responding disease after 16 weeks of first-line treatment and 69 were randomised using a 2 : 1 ratio: 44 to adavosertib and 25 to active monitoring.

FIGURE 4 Flow of patients through the trial. CR, complete response; PR, partial response; RECIST, response evaluation criteria in solid tumours. (Figure not reproduced here; see the original article.)

Owing to the COVID-19 pandemic, the trial was suspended in March 2020 just before reaching the required number of control arm PFS events (n = 26) to trigger final analysis. Given that recruitment had been planned to close in May 2020, the FOCUS4 IDMC were asked to review the efficacy data in a closed meeting to determine whether recruitment should re-open or whether the trial could close on the grounds of adequate data for determining any signal of drug activity. The IDMC recommended the latter and, following endorsement by the TSC, recruitment was formally closed. Follow-up and data cleaning continued to October 2020, when database lock took place.

A summary of the patients’ baseline characteristics is presented in Table 8. There were several minor imbalances favouring the adavosertib arm, which were corrected for in the adjusted analysis (primary model). More patients in the active monitoring arm than in the adavosertib arm had two or more metastatic sites and an unresected primary tumour. There were no differences in the frequency of other molecular alterations between the arms.

There were no significant differences in the registration period chemotherapy regimens used between the adavosertib arm and the active monitoring arm. Of the 69 randomised patients, 22 (32%) received leucovorin, fluorouracil and oxaliplatin (FOLFOX), 22 (32%) received leucovorin, fluorouracil and irinotecan (FOLFIRI), 17 (25%) received CAPOX, and 6 (9%) received leucovorin, fluorouracil, oxaliplatin and irinotecan (FOLFOXIRI) (see Table 8). Slightly more patients in the active monitoring arm than in the adavosertib arm had stable disease at the end of first-line chemotherapy (48% vs. 39%, respectively).

Progression-free survival (per protocol)

Five patients were excluded from the per-protocol analysis: four patients did not start treatment (adavosertib arm) and one patient was found to have had progressive disease at the point of randomisation and was, therefore, not eligible (active monitoring arm). One patient was censored early when they received fluorouracil as an anti-cancer treatment prior to progression (active monitoring arm).

Within the primary per-protocol analysis (n = 64), there were 40 PFS events in the adavosertib arm (n = 40 patients) and 22 PFS events in the active monitoring arm (n = 24 patients). Patients treated with adavosertib had a longer PFS than those on active monitoring (3.61 vs. 1.87 months, respectively). Both the unadjusted (HR 0.52, 95% CI 0.30 to 0.89; p = 0.022) and the adjusted (HR 0.35, 95% CI 0.18 to 0.68; p = 0.0022) analysis were statistically significant. Kaplan-Meier curves are presented in Figure 5.

FIGURE 5 Kaplan–Meier curves for PFS in the per-protocol analysis. (Figure not reproduced here; see the original article.)

Progression-free survival (intention to treat)

All patients were included in the ITT analysis but four patients were censored the day after randomisation: three patients in the adavosertib arm (two because of patient withdrawal and one without any post-randomisation CT scan assessments) and one in the active monitoring arm without any post-randomisation CT scan assessments.

There were 41 PFS events in the adavosertib arm (n = 44 patients) and 23 PFS events in the active monitoring arm (n = 25 patients). Consistent with the per-protocol analysis, the ITT PFS analysis showed a PFS advantage of adavosertib compared with active monitoring in both the unadjusted (HR 0.55, 95% CI 0.32 to 0.94; p = 0.032) and the adjusted (HR 0.40, 95% CI 0.21 to 0.75; p = 0.0051) analysis.

Overall survival (intention to treat)

There were 27 deaths in the adavosertib arm (n = 44 patients) and 16 deaths in the active monitoring arm (n = 25 patients). There was no significant OS benefit of adavosertib compared with active monitoring (median survival 14.0 vs. 12.8 months, respectively) (unadjusted HR 0.79, 95% CI 0.42 to 1.48; p = 0.47) (adjusted HR 0.92, 95% CI 0.44 to 1.94; p = 0.93).

Tumour control

Adavosertib was associated with a higher proportion of patients with disease control than active monitoring (47% vs. 28%, respectively, at any time during the trial), including one patient with a documented partial response to adavosertib.

Subgroup analyses

The impact of adavosertib compared with active monitoring on PFS was explored in prespecified subgroups (Figure 6). The most marked difference in adavosertib effect was for the site of the primary tumour location (PTL); patients with a right PTL had no PFS advantage with adavosertib compared with active monitoring (1.87 vs. 1.91 months, respectively; HR 1.02, 95% CI 0.41 to 2.56), whereas those with a left PTL did have a PFS advantage (3.61 vs. 1.87 months, respectively; HR 0.24, 95% CI 0.11 to 0.51) (interaction p = 0.043) (Figures 7 and 8).

FIGURE 6 Subgroup analyses for PFS by ITT. WHO, World Health Organization. (Figure not reproduced here; see the original article.)

FIGURE 7 Kaplan–Meier curves for PFS (ITT) by PTL: (a) left sided (n = 47); and (b) right sided (n = 22). (Figure not reproduced here; see the original article.)

FIGURE 8 Swimmer plot by randomised group and location of primary tumour. Light-blue horizontal strip, right sided; navy strip, left sided (including rectum). (Figure not reproduced here; see the original article.)

This prompted an unplanned subgroup analysis of PTL on OS and, despite that the number of events was small, the interaction was even more marked. The median OS was 14.1 versus 11.3 months for adavosertib versus active monitoring, respectively, for left PTL (adjusted HR 0.40, 95% CI 0.17 to 0.97), but was 6.5 versus 15.5 months, respectively, for right PTL (HR 6.46, 95% CI 1.34 to 33.6) (interaction p = 0.0032). In terms of response, 38% of right-sided adavosertib patients compared with 42% of right-sided active monitoring patients reported disease stability or response at least once while on the trial, whereas for left-sided tumours the figures were 53% compared with 19%, respectively.

Patients who had responded to induction chemotherapy (vs. stable disease) and who had two or more metastatic sites appeared to benefit more from adavosertib, albeit to a lesser degree than those with only one metastatic site (interaction p = 0.14 for response to induction; p = 0.12 for number of metastatic sites) (see Figure 6).

External analyses to further characterise the RAS/TP53-mutant biomarker population

To the best of our knowledge, the RAS/TP53-mutant population has not been previously described. To understand the prognostic implication of this alteration, we analysed the outcomes of a subset (n = 438) of the FOCUS trial in whom the S:CORT consortium30 had analysed a wider panel of CRC genes, including KRAS, NRAS, BRAF, MSI and TP53. The RAS/RAF wild-type group was the reference population (median OS 21.6 months). The RAS/TP53-mutant population was distinct from and had a worse prognosis than the population with either mutation alone (RAS or TP53), with a median OS of 14.9 months (HR 2.06, 95% CI 1.08 to 3.93; p = 0.028). This suggests that the RAS/TP53-mutant population constitutes a poor prognosis subgroup, but the prognosis is not as poor as it is for patients with a BRAF-mutant or MSI-high tumour.

Effect of RAS and TP53 mutation subtypes on adavosertib activity

We observed that patients with KRAS codon 12/13 mutations (n = 51) experienced a significant benefit from adavosertib (interaction p = 0.004), whereas no detectable benefit was observed in those with KRAS mutations at other codons or with NRAS mutation (n = 18). Furthermore, the interaction effects of KRAS subtype and of PTL on PFS may be additive, as there is a significant benefit from adavosertib within the subgroup of left PTL KRAS codon 12/13 subtypes (HR 0.19, 95% CI 0.08 to 0.48) and a potential disbenefit within the subgroup of right PTL non-codon 12/13 subtypes (HR 3.93, 95% CI 0.42 to 36.69) (Figure 9). The subtype of TP53 mutation or the co-occurrence of PIK3CA mutation did not affect the outcome.

FIGURE 9 Forest plot for PFS (ITT) by PTL and KRAS codon 12/13 status. (Figure not reproduced here; see the original article.)

Toxicity and compliance

There was good compliance with the randomised allocation, and adavosertib was well tolerated but with some increased toxicity. Adavosertib was associated with an increase in reported toxicity (grade 1 or worse) compared with active monitoring, most notably increased frequency of diarrhoea (61% vs. 28%, respectively), fatigue (75% vs. 56%), nausea (68% vs. 32%) and vomiting (41% vs. 4%). However, the majority of such toxicity was of low grade; in the adavosertib arm, 9% of patients reported diarrhoea, 11% reported fatigue, 5% reported nausea and 2% reported vomiting of grade 3 or worse, compared with no patients in the active monitoring arm.

Impact of adavosertib dosing

There was an increase in the dose of adavosertib from 250 mg to 300 mg during the trial. PFS was 2.2 months (HR 0.58, 95% CI 0.31 to 1.06) for the 250-mg dose and 3.7 months (HR 0.47, 95% CI 0.25 to 0.89) for the 300-mg dose; this difference was non-significant (p = 0.48). The increase in dose from 250 mg to 300 mg was associated with an increased frequency of grade 3 diarrhoea (4% vs. 14%, respectively), but otherwise the toxicity profile was similar. Rates of dose modifications were similar at doses of 250 mg and 300 mg: dose delays 16% vs. 7%, respectively; dose reductions 4% vs. 5%; and dose omissions 19% vs. 17%.

Discussion and conclusions

FOCUS4-C met its primary end point: patients with RAS/TP53-mutant metastatic CRC had a PFS advantage with adavosertib compared with active monitoring following induction chemotherapy. This activity was clearly limited to patients with left PTL. An assessment of the impact on longer-term outcomes showed an OS benefit with adavosertib compared with active monitoring in RAS/TP53-mutant patients with left PTL. These results are particularly encouraging because patients with RAS/TP53-mutant metastatic CRC are a poor prognostic population and have limited treatment options. Adavosertib was well tolerated at both of the doses evaluated, and it is possible that nearly half of the adavosertib patients were dosed suboptimally (250 mg once daily instead of 300 mg once daily). It is encouraging that a clear efficacy signal was reached for both doses despite the forced early closure as a result of the COVID-19 pandemic.

The overarching aim of the FOCUS4 trial programme was to test novel agents efficiently with specified biomarker subgroups in metastatic CRC using a ‘window of opportunity’ following 16 weeks of induction chemotherapy, with the MAMs design allowing for an early signal of drug inactivity.13 FOCUS4-C represents the success of this approach, utilising a PFS end point and control arm. The intermittent treatment strategy employed in FOCUS4 follows the demonstration of no detriment in OS in the MRC COIN trial, which has been further substantiated by an individual patient data (IPD) meta-analysis.35 Therefore, we designed FOCUS4 to specifically use this window following first-line induction chemotherapy to test novel agents in biomarker-specified groups, prior to the evolution of multiple resistance mechanisms.13

Wee1 inhibition induces failure of the G₂ and intra-S-phase checkpoints, which increases the reliance on the G₁/S checkpoint, and deoxyribonucleotide triphosphate shortage due to unscheduled replication fork firing, which further exacerbates replication stress during S-phase. Tumours containing RAS mutations, which drive replication stress and loss of G₁ checkpoint control subsequent to loss of TP53 function, were hypothesised to benefit from this treatment.

Although the clinical implications of the RAS/TP53 mutation in metastatic CRC are not well studied, each alteration is individually well characterised. FOCUS4-C has shown that the double-mutant subgroup carries a moderately poor prognosis, which is largely driven by the KRAS mutation. Other approaches to targeting KRAS-mutant tumours include inhibition of the G18C mutation specifically; we show here that patients in FOCUS4-C have a similar benefit with adavosertib as those treated in a Phase I trial with sotorasib (Lumakras, Amgen), a promising small molecule targeting KRAS p.G12C (PFS 3.6 vs. 4 months).84

There was marked and significant heterogeneity in the benefit of adavosertib by PTL and KRAS mutation subtype. Adavosertib activity was limited to left colon and rectal PTL, with little activity observed in right PTL. Although the analysis by PTL was prespecified, the analysis by KRAS mutation subtype was not prespecified. Having observed the significant subgroup effects on PFS, the impact on OS was assessed. It is interesting to see that OS was significantly improved in patients with left-sided tumours, with an increase in median OS from randomisation from 11.3 months to 14.1 months (HR 0.40, 95% CI 0.17 to 0.97). There is also a possibility that adavosertib may adversely affect outcome in patients with right PTL. However, the numbers of patients and events were limited and, therefore, any conclusions in relation to this observed effect on OS.need to be drawn with caution. Differences in CRC by PTL are well documented in terms of biology, prognosis and treatment response, and ongoing translational studies may provide a molecular basis for this observation. In addition, adavosertib had the most PFS effect in patients with KRAS codon 12,13-/TP53-mutant tumours, with lesser effect in those patients with extended KRAS or NRAS mutations; functional differences between RAS isoforms are documented.85

Adavosertib has demonstrated an acceptable safety profile; the main toxicity was diarrhoea. There was only minimal additional toxicity when the dose was increased from 250 mg to 300 mg, and a suggestion of additional activity with the higher dose. The 300-mg dosing is, therefore, recommended to progress to further clinical studies.

Alterations in the DDR are emerging as novel targets for cancer therapeutics, with notable successes with poly (ADP -ribose) polymerase inhibitors in pancreatic and ovarian cancers that harbour breast cancer gene mutations68,69 or with defects in other genes belonging to the human hairless gene family, as seen in prostate cancer.86 This strategy is less developed in CRC, but the prevalence of alterations in DDR genes are estimated to be between 10% and 30%87 and more frequent in the MSI-high subgroup. One limitation has been the lack of standard assays to identify CRC tumours harbouring clinically relevant DDR defects. The studies of poly (ADP -ribose) polymerase inhibitors in CRC have been limited by lack of patient selection and toxicity with chemotherapy combinations; promising preclinical work may serve the basis for further therapeutic development.14

Adavosertib has been tested in multiple tumour sites as monotherapy or in combination with radiotherapy or chemotherapy.73,74 Disappointing results have been observed in unselected populations. However, clinical benefit was recently shown from the combination of adavosertib plus gemcitabine compared with gemcitabine alone in high-grade serous ovarian cancer, a TP53-mutated tumour type with high replication stress, similar to our selected population.73 FOCUS4-C has highlighted the importance of optimisation of patient selection for therapeutics targeting the DDR.

There are limitations to this study. FOCUS4-C was not placebo controlled because of the requirement of premedication with dexamethasone and a 5HT3 inhibitor owing to concerns regarding adavosertib toxicity. It is possible, therefore, that the PFS effect observed was influenced by investigator and patient preference to restart first-line chemotherapy sooner in the active monitoring arm. However, a marked difference in effect was observed between the right and the left PTL groups treated with adavosertib, suggesting a lesser effect on the primary analysis owing to this potential bias.

Although these studies were not designed or powered for cross-study comparison, comparison of the effect of maintenance capecitabine (in FOCUS4-N) compared with adavosertib within a RAS/TP53-mutant population shows similar effect (PFS HR 0.44, 95% CI 0.30 to 0.63). However, the purpose of FOCUS4-C was to demonstrate activity of adavosertib within a biomarker-selected population, which has been achieved. Adavosertib has shown similar efficacy to capecitabine, the most active agent in CRC, within this poor prognosis subgroup, and this is promising for its further use in this disease.

Further clinical development is warranted given the efficacy and safety profile demonstrated, particularly within a population of unmet need. Translational work to understand the mechanism of this response and resistance is ongoing by the S:CORT30 and ACRCelerate31 programmes. Suggestions for development include other stages of the clinical pathway (treatment resistant setting) as monotherapy, in combination with other agents, or in combination with radiotherapy.