Survival benefit to immunotherapy according to site of organ involvement in metastatic anal cancer.

3 Background: For patients with metastatic anal cancer, demonstration of anti-tumor activity by anti-PD-(L)1 antibodies has expanded the treatment landscape. To date, there are no predictive biomarkers associated with clinical benefit to immunotherapy in this setting. In the absence of clinical trials directly comparing chemotherapy and immunotherapy for metastatic anal cancer, the optimal sequencing of therapeutic lines remains undefined because historical series have been limited to cytotoxic chemotherapy. We evaluated the survival outcomes of patients with metastatic anal cancer following treatment with immunotherapy and with chemotherapy. Methods: We reviewed retrospectively the MD Anderson Cancer Center database for patients with unresectable and/or metastatic anal cancer diagnosed between 6/2014 and 11/2021. Median survival was estimated using the Kaplan-Meier method and compared between subpopulations of interest with a log-rank test. Results: Among 82 patients with metastatic anal cancer, 68 (83%) were female, and the median age was 60 years (range, 39-81). With a median follow-up time of 24.6 months, the median lines of systemic therapy were 2 (range, 1-5). 58 (71%) received anti-PD-(L)1 immunotherapy, either alone (N=51) or in combination with bevacizumab or with MEDI-0457 on a clinical trial (N=7). Median progression-free survival times (PFS) for lines 1, 2, and 3 of systemic therapy were 7.2 months (95% CI (Confidence Interval) 5.3-9.1; N=82), 3.6 months (95% CI 2.4-4.8; N=58), and 4.1 months (95% CI 2.8-5.4; N=34), respectively. In the treatment-refractory setting, no difference in median PFS between chemotherapy and immunotherapy was observed (4.7 months vs 2.9 months, respectively; hazard ratio (HR) 0.9, 95% CI 0.5-1.4); p=.17). Median overall survival (OS) was estimated at 33.9 months (95% CI, 24.0-34.8). For patients with metastatic anal cancer treated with immunotherapy, involvement of only distant lymph nodes (N=10/58, 17%) was associated with improved median PFS (11.3 months vs 2.8 months; HR 3.5, 95% CI 1.8-6.6; p=.002) and median OS (45.2 months vs 27.1 months; HR 2.9, 95% CI 1.3-6.5, p=.02) than other sites of distant organ involvement (N=48/58, 83%). Conclusions: In this single-institution retrospective study at a large academic referral center, both chemotherapy and immune checkpoint blockade were effective treatment options for patients with metastatic anal cancer. These data provide historical context in estimating median PFS necessary for future trial design in patients with metastatic anal cancer. Lymph node-only distribution of distant metastatic disease was predictive for improved survival with immunotherapy. Pending further validation, these data provide novel identification of a potential predictive factor associated with benefit to immunotherapy in patients with metastatic anal cancer.