Usefulness of Flow Cytometry for the Detection of Cutaneous Localization in Malignant Hematologic Disorders

BACKGROUND: Histological evaluation of malignant hematologic involvement of the skin can be challenging and needs an extended immunohistochemistry panel. We assessed the ability of flow cytometry (FCM) to detect neoplastic cell subsets in skin biopsies as a useful tool that supplements the histological examination in a complementary way. METHODS: Two hundred and forty-three consecutive skin biopsies were retrospectively analyzed between April 2012 and July 2017. RESULTS: Among them, 147 samples, corresponding to 128 patients, were analyzed at diagnosis. Eighty-seven patients had erythrodermic inflammatory dermatoses, and 41 patients had cutaneous hematologic neoplasms. Cutaneous T-cell lymphomas were the most frequent disorders, accounting for 70% of cases (29/41). Cutaneous B-cell lymphoma was found in only 17% of cases (7/41) and immature hematologic malignancies in 5% (2/41). Three patients had secondary skin involvement. The sensitivity of FCM skin biopsy analysis was 78.1% (32/41). Among the 243 samples, 27 patients had mycosis fungoides (MF) or Sezary syndrome (SS) with available FCM data. A loss of CD26 expression was identified in 92% of cases of transformed MF or SS versus 40% of cases of non-transformed MF (P = 0.0057 χ²). Among the 12 MF patients with negative CD26 expression, six progressed to SS versus none in the positive group (50% vs. 0% P = 0.0168 χ²). CONCLUSIONS: FCM analysis of the skin biopsies is a sensitive method and a useful tool for improving the sensitivity of diagnosis of hematologic skin neoplasms. Among the MF patients, a loss of CD26 expression could be a marker of higher risk of progression. © 2019 International Clinical Cytometry Society.