Abstract

Background: Scalp melanomas present a challenge for accurate Breslow thickness measurement given the dense follicular presence/involvement. A classification system of follicular/folliculotropic melanomas has been proposed by Tjarks et al. in which 3 distinct patterns of involvement are identified: primary follicular, folliculotropic, and invasive arising from melanoma in situ (MIS) with extensive follicular involvement. The applicability of this system to scalp melanomas has not yet been delineated. Methods: File archives at our institution were searched for primary scalp melanomas diagnosed between January 1, 2010 and December 31, 2020, excluding cases with lack of archival material for review and metastatic melanoma. Two pathologists assessed all cases and applied Tjarks classification. Clinicopathologic data was recorded from the electronic medical record for correlation. Results: 54 cases were identified from 46 male (85%) and 8 female (15%) patients. The average age was 67.3 years (± 4.9 years). Mean follow-up time was 2.98 years post-resection. 44 (81%) cases showed follicular involvement, as follows: 15 MIS only; 10 arising from MIS with invasive follicular involvement; and 19 folliculotropism. No primary folliculotropic melanomas were identified. Follicular destruction was observed in 17 of 29 follicular-involved invasive melanomas. Progressive follicular involvement was associated with an increased risk of death (36% vs. 20% no involvement), whereas follicular destruction alone showed no association with mortality. Accurate determination of the modified follicular Breslow thickness was either irrelevant or inconsistent in the vast majority of cases. Conclusion: The Tjarks classification can be applied to scalp melanomas and may provide valuable insight in prognosis.

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