Epidemiology, clinical characteristics, treatment, and outcomes of proliferating pilar tumors: A systematic review

Background: Proliferating pilar tumors (PPTs) are rare cutaneous neoplasms arising from hair follicles that have both malignant and metastatic potential. Objective: To present a systematic review of the epidemiology, clinical characteristics, and treatment and outcome data on PPTs. Methods: Using the OVID platform, MEDLINE and Embase were searched from inception until May 26, 2022. All studies that provided original data on PPTs in English were included. References of these studies were also cross-checked to identify any additional relevant articles. Oxford's Levels of Evidence-Based Medicine was used for quality assessment. Results: A total of 114 articles, providing data on 361 cases of PPTs, were included in our synthesis. Every study included was either a case series or case report. The mean age at diagnosis was 61.7. Most patients in the synthesis were female (71%), and the majority of cases occurred on the scalp (73.1%). The presence or absence of cytological atypia was only reported in one-third of the cases; 36.8% of cases were classified as malignant and 7.5% metastasized. Although no lesions treated with Mohs micrographic surgery required adjuvant radiation and only one reported recurrence occurred after Mohs surgery, there is insufficient data to make conclusions on a superior treatment modality. Limitations: All studies in this review were either case reports or case series. Conclusions and Relevance: Our study supports the notion that PPTs occur most commonly on the scalp of elderly female patients. Moreover, our findings confirm that PPT is capable of demonstrating aggressive biology and metastasis. Given the lack of uniformity in histologic description, pathologists should be encouraged to comment on the presence and degree of cytological atypia when reporting cases of rare neoplasms such as the PPT. Greater consensus on diagnosis and classification as well as more robust data is needed regarding optimal management.