A population-level analysis of nonsquamous penile cancer: The importance of histology.

Background: Nonsquamous penile cancers comprise 5% of penile malignancies, though their clinicopathologic features and prognostic significance remain unknown. We used a national cancer registry to detail clinical characteristics and compare cancer-specific mortality (CSM) of nonsquamous cancers with squamous cell carcinoma (SCC).
Methods: The Surveillance, Epidemiology, and End Results (SEER) database (1975-2016) was queried to identify adults with nonsquamous penile cancer and penile SCC. Multivariable Fine and Gray competing-risks regression, propensity score matching, and cumulative incidence plots were used.
Results: 666 men with nonsquamous penile cancer and 5,894 men with penile SCC were identified. The most commonly represented nonsquamous histological subtypes were Kaposi sarcoma (n = 183, 27.5%), melanoma (n = 74, 11.1%), basal cell carcinoma (n = 65, 9.8%), and extramammary Paget disease (n = 42, 6.3%). Cumulative incidence plots revealed a 10-year CSM rate of 32.6% in the nonsquamous penile cancer group and 25.6% in the matched penile SCC group (P < 0.0001). Among Kaposi sarcoma patients and matched SCC patients, we found a 10-year CSM rate of 29.6% in the Kaposi sarcoma group and 15.3% in the penile SCC group (P = 0.002). Similarly, a comparison of penile melanoma patients with matched SCC patients revealed a 10-year CSM rate of 38.4% in the melanoma group and 16.6% in the SCC group (P = 0.002). There was no difference in CSM between patients with basal cell carcinoma and SCC. In a sensitivity analysis limiting year of diagnosis to 2000 and onward, we found no difference in CSM between the general nonsquamous cohort or the Kaposi sarcoma cohort and matched SCC patients, but contemporary melanoma patients maintained worse CSM with a 10-year rate of 38.4% vs. 15.8% in matched SCC patients (P = 0.045).
Conclusions: The most common nonsquamous penile cancers are Kaposi sarcoma, melanoma, and basal cell carcinoma. Overall, CSM is higher in nonsquamous penile cancers as compared to stage-matched SCC. Outcomes are similar in modern patients, likely due to improved control of systemic HIV in patients with Kaposi sarcoma. However, men with penile melanoma continue to experience a higher rate of CSM.
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