Longitudinal circulating tumor DNA monitoring for detection of molecular residual disease in patients with penile squamous cell carcinoma.

Abstract

11 Background: Penile squamous cell carcinoma (SCC) is an extremely rare, aggressive disease, representing 0.4-0.6% of all malignancies in males in the U.S. and Europe. Early diagnosis is imperative, as lymphatic spread is associated with a dismal prognosis. The estimated 5-year survival rate in patients with pelvic lymph node involvement is 0%. Moreover, there are limited treatment options that carry significant toxicity risks. Accurate biomarkers to evaluate treatment response and guide treatment to improve outcomes are needed. Molecular residual disease monitoring with circulating tumor DNA (ctDNA) may be helpful in these scenarios. Methods: This is a retrospective analysis of a cohort of 7 patients with advanced HPV-unassociated penile SCC treated at Rush University Medical Center who monitored closely for molecular residual disease (MRD). Signatera (Natera Inc.), a personalized tumor-informed ctDNA assay, was utilized for detection and quantification of ctDNA in patients’ plasma samples, measured at regular intervals. Progression of disease was based on radiographic imaging. Results: In our cohort, personalized, tumor-informed ctDNA assays were designed for 100% (7/7) of the patients. ctDNA was detectable in at least one time point in all of the patients. One patient underwent partial penectomy and lymph node (LN) dissection with 1/11 LN involved. He is being monitored without adjuvant treatment and has sustained ctDNA clearance. Another patient underwent surgery, and had positive post-operative ctDNA. He was treated with adjuvant TIP (paclitaxel, ifosfamide, and cisplatin) with subsequent ctDNA clearance. In 3 of the patients, ctDNA was checked at regular intervals and rising ctDNA prompted imaging studies that showed progression. These patients proceeded to second line treatment options. The remaining 2 patients are non-surgical candidate with LN positivity, who will begin treatment with TIP and monitoring of ctDNA after each cycle of chemotherapy. Twenty-eight percent (2/7) of patients remain alive with sustained ctDNA clearance. Twenty-eight percent (2/7) of patients remain alive with ctDNA positivity, planned to initiate treatment and monitoring of ctDNA at regular intervals. Forty-three percent (3/7) of patients who had persistent ctDNA positivity are now deceased. Conclusions: Our data suggests that a personalized, tumor-informed ctDNA assay is not only useful for MRD monitoring, but also highly predictive of treatment response and imaging-based progression in patients with penile SCC. In our sample, MRD status correlated with both radiographic progression and clinical outcomes. Prospective studies are needed to better understand how ctDNA can be used to guide neoadjuvant and adjuvant approaches, including treatment intensification or de-escalation, in patients with penile SCC.