Impact of molecular tumour board discussion on targeted therapy allocation in advanced prostate cancer.

BACKGROUND: Molecular tumour boards (MTB) optimally match oncological therapies to patients with genetic aberrations. Prostate cancer (PCa) is underrepresented in these MTB discussions. This study describes the impact of routine genetic profiling and MTB referral on the outcome of PCa patients in a tertiary referral centre. METHODS: All PCa patients that received next-generation sequencing results and/or were discussed at an MTB between Jan 1, 2017 and Jan 1, 2020 were included. Genetically matched therapies (GMT) in clinical trials or compassionate use were linked to actionable alterations. Response to these agents was retrospectively evaluated. RESULTS: Out of the 277 genetically profiled PCa patients, 215 (78%) were discussed in at least one MTB meeting. A GMT was recommended to 102 patients (47%), of which 63 patients (62%) initiated the GMT. The most recommended therapies were PARP inhibitors (n = 74), programmed death-(ligand) 1 inhibitors (n = 21) and tyrosine kinase inhibitors (n = 19). Once started, 41.3% had a PFS of ≥6 months, 43.5% a PSA decline ≥50% and 38.5% an objective radiographic response. CONCLUSION: Recommendation for a GMT is achieved in almost half of the patients with advanced prostate cancer, with GMT initiation leading to durable responses in over 40% of patients. These data justify routine referral of selected PCa patients to MTB's.

Impact of DNA damage repair defects and aggressive variant features on response to carboplatin-based chemotherapy in metastatic castration-resistant prostate cancer.

Platinum-based chemotherapy is not standard of care for unselected or genetically selected metastatic castration-resistant prostate cancer (mCRPC) patients. A retrospective assessment of 71 patients was performed on platinum use in the Netherlands. Genetically unselected patients yielded low response rates. For a predefined subanalysis of all patients with comprehensive next-generation sequencing, 30 patients were grouped based on the presence of pathogenic aberrations in genes associated with DNA damage repair (DDR) or aggressive variant prostate cancer (AVPC). Fourteen patients (47%) were DDR deficient (DDRd), of which seven with inactivated BRCA2 (BRCA2mut). Six patients classified as AVPC. DDRd patients showed beneficial biochemical response to carboplatin, largely driven by all BRCA2mut patients having >50% prostate-specific antigen (PSA) decline and objective radiographic response. In the wild-type BRCA2 subgroup, 35% had a >50% PSA decline (P = .006) and 16% radiographic response (P < .001). Median overall survival was 21 months for BRCA2mut patients vs 7 months (P = .041) for those with functional BRCA2. AVPC patients demonstrated comparable responses to non-AVPC, including a similar overall survival, despite the poor prognosis for this subgroup. In the scope of the registration of poly-(ADP)-ribose polymerase inhibitors (PARPi) for mCRPC, we provide initial insights on cross-resistance between PARPi and platinum compounds. By combining the literature and our study, we identified 18 patients who received both agents. In this cohort, only BRCA2mut patients treated with platinum first (n = 4), responded to both agents. We confirm that BRCA2 inactivation is associated with meaningful responses to carboplatin, suggesting a role for both PARPi and platinum-based chemotherapy in preselected mCRPC patients.

Early On-treatment Circulating Tumor DNA Measurements and Response to Immune Checkpoint Inhibitors in Advanced Urothelial Cancer.

BACKGROUND: Immune checkpoint inhibitors (ICIs) can induce durable disease control in metastatic urothelial cancer (mUC), but only 20-25% of patients respond. Early identification of a nondurable response will improve management strategies. OBJECTIVE: To investigate whether on-treatment circulating tumor DNA (ctDNA) measurements can predict ICI responsiveness in mUC patients. DESIGN, SETTING, AND PARTICIPANTS: This study consists of a discovery cohort of 40 mUC patients and a prospective multicenter validation cohort of 16 mUC patients. Plasma cell-free DNA was collected at baseline and after 3 and 6 wk on ICIs. The ctDNA levels were calculated from targeted sequencing. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Outcome measurements were progression-free survival (PFS), overall survival (OS), and nondurable response (PFS ≤6 mo). Relationships with ctDNA were assessed using Cox regression. Changes in ctDNA level at 3 and 6 wk were categorized by an increase or decrease relative to baseline. RESULTS AND LIMITATIONS: In the discovery cohort, ctDNA was detected in 37/40 (93%) of patients at baseline. A ctDNA increase was observed in 12/15 (80%) and ten of 12 (83%) patients with a nondurable response at 3 and 6 wk, respectively. Of patients with a durable response (PFS >6 mo), 94% showed a decrease. A ctDNA increase at 3 wk was associated with shorter PFS (hazard ratio [HR] 7.8, 95% confidence interval [CI] 3.1-19.5) and OS (HR 8.0, 95% CI 3.0-21.0), independent of clinical prognostic variables. Similar results were observed at 6 wk. The 3-wk association with PFS was validated in a prospective cohort (HR 7.5, 95% CI 1.3-42.6). Limitations include the limited number of patients. CONCLUSIONS: Early changes in ctDNA levels are strongly linked to the duration of ICI benefit in mUC and may contribute to timely therapy modifications. PATIENT SUMMARY: Benefit from immunotherapy can be predicted after only 3 wk of treatment by investigating cancer DNA in blood. This could help in timely therapy changes for urothelial cancer patients with limited benefit from immunotherapy.

Cross-Resistance between Platinum-Based Chemotherapy and PARP Inhibitors in Castration-Resistant Prostate Cancer.

Patients with metastatic castration-resistant prostate cancer (mCRPC) harbouring homologous recombination repair-related gene aberrations (HRRm) can derive meaningful benefits from both platinum-based chemotherapy (PlCh) and PARP inhibitors (PARPi). Cross-resistance between these agents is well-recognised in other tumour types but data on prostate cancer is lacking. In this retrospective pre-planned study, we assessed 28 HRRm mCRPC patients who received PlCh and PARPi. Progression-free survival (PFS) on initial therapy was longer than on subsequent therapy (median 5.3 vs. 3.4 months, p = 0.016). The median PFS of PlCh was influenced by the order of agents, with 3.6 months shorter PFS after PARPi than when administered first. The median PFS of PARPi was less influenced, with 0.9 months shorter PFS after PlCh than before. In the PARPi-first subgroup, six out of 16 evaluable patients (37.5%) had a >50% PSA decline to PlCh, and two of eight (25.0%) had a radiographic response to PlCh. In the PlCh-first subgroup, 6/10 (60.0%) had a >50% PSA decline, and 5/9 (55.6%) had a radiographic response to PARPi. These data show >40% of the cohort is sensitive to a subsequent HRR-targeting agent. PlCh appears to induce less cross-resistance than PARPi. Additional data on resistance mechanisms will be crucial in defining an optimal treatment sequence in HRRm mCRPC patients.

Responsiveness to Immune Checkpoint Inhibitors Is Associated With a Peripheral Blood T-Cell Signature in Metastatic Castration-Resistant Prostate Cancer.

PURPOSE: Although most patients with microsatellite instable (MSI) metastatic castration-resistant prostate cancer (mCRPC) respond to immune checkpoint blockade (ICB), only a small subset of patients with microsatellite stable (MSS) tumors have similar benefit. Biomarkers defining ICB-susceptible subsets of patients with MSS mCRPC are urgently needed. METHODS: Using next-generation T-cell repertoire sequencing, we explored immune signatures in 54 patients with MSS and MSI mCRPC who were treated with or without ICB. We defined subset-specific immune metrics as well as T-cell clusters and correlated the signatures with treatment benefit. RESULTS: Consistent overlaps between tumor and peripheral T-cell repertoires suggested that blood was an informative material to identify relevant T-cell signatures. We found considerably higher blood T-cell richness and diversity and more shared T-cell clusters with low generation probability (pGen) in MSI versus MSS mCRPC, potentially reflecting more complex T-cell responses because of a greater neoepitope load in the MSI subset. Interestingly, patients with MSS mCRPC with shared low pGen T-cell clusters showed significantly better outcomes with ICB, but not with other treatments, compared with patients without such clusters. Blood clearance of T-cell clusters on ICB treatment initiation seemed to be compatible with T-cell migration to the primary tumor or metastatic sites during the process of clonal replacement as described for other tumors receiving ICB. CONCLUSION: The MSI mCRPC subset shows a distinct T-cell signature that can be detected in blood. This signature points to immune parameters that could help identify a subset of patients with MSS mCRPC who may have an increased likelihood of responding to ICB or to combination approaches including ICB.