Follicular mucinosis in patients with hematologic malignancies other than mycosis fungoides: A clinicopathologic study

Background: Follicular mucinosis (FM), which is defined by mucin accumulation within follicular epithelium, may occur in mycosis fungoides (MF). FM without MF is occasionally reported in systemic hematologic malignancies and may be diagnostically challenging. Objective: To describe clinicopathologic characteristics of FM in patients with hematologic malignancies other than MF. Methods: Clinical data and histopathology features were analyzed in patients with FM and hematologic malignancies diagnosed between 1994 and 2017. Results: A total of 18 patients with FM and systemic hematologic malignancies without cutaneous T-cell lymphoma (CTCL) were identified; 9 of them were discovered after hematopoietic stem cell transplantation. No patients with non–CTCL-associated FM (n = 46 [37 biopsy specimens]) developed CTCL during a mean follow-up of 4.3 years. Of the cases of CTCL associated with FM (n = 44 [31 biopsy specimens]), MF was the most common subtype (n = 38), although other CTCLs were identified. FM in patients with non-CTCL hematologic malignancies differed clinically from those with MF-associated FM, presenting most frequently with erythematous papules (P < .0001), without plaques (P <.0001), without alopecia (P = .001), and without histopathologically identified epidermal exocytosis (P = .013). Limitations: A retrospective study in a single cancer center. Conclusions: FM can present in systemic hematologic malignancies, including after hematopoietic stem cell transplantation. Papular lesional morphologic and histopathologic features may help to distinguish these cases from MF.