Prognostic and Predictive Markers for Patients With Anal Cancer

Squamous cell carcinoma of the anus and anal canal is a rare malignancy with an increasing incidence in the United States. In the past 2 decades, the proportion of Americans diagnosed with incurable, metastatic anal cancer at the time of initial presentation has increased. Most cases are linked to prior infection with HPV. Although concurrent chemoradiotherapy has been the accepted standard treatment for patients with localized anal cancer over the past half century, therapeutic advances have increased options for patients with unresectable or incurable anal cancer over the past 5 years. Specifically, combination chemotherapy and immunotherapy with anti–PD-(L)1 antibodies has demonstrated efficacy in this setting. Greater understanding of molecular drivers of this viral-associated malignancy has provided critical insight into evolving biomarkers for the clinical management of anal cancer. The pervasiveness of HPV across cases of anal cancer has been leveraged for the development of HPV-specific circulating tumor DNA assays as a sensitive biomarker for prognosticating recurrence in patients with localized anal cancer who complete chemoradiation. For patients with metastatic disease, somatic mutations, well-characterized for anal cancer, have not shown utility in identifying patients who benefit from systemic treatments. Although the overall response rate to immune checkpoint blockade therapies is low for metastatic anal cancer, high immune activation within the tumor and PD-L1 expression may identify patients more likely to experience response. These biomarkers should be incorporated into the design of future clinical trials to personalize further treatment approaches in the evolving management of anal cancer.