Mycosis fungoides in plaque stage with pronounced eosinophilic infiltration, folliculotropism, and concomitant invasive squamous cell carcinoma.

Mycosis fungoides (MF) is a relatively rare cutaneous T-cell malignancy. Only two cases of MF with marked eosinophilia have been reported. In addition, MF with concomitant squamous cell carcinoma (SCC) occurring in the site of MF has not been reported. The author reports herein a very rare case of MF in the plaque stage showing pronounced eosinophilic infiltration, folliculotropic pattern, and in situ development of poorly differentiated squamous cell carcinoma (SCC). A 75-year-old man was found to show high prostate specific antigen (PSA, 13 hg/ml) and prostatic biopsy showed well differentiated prostatic adenocarcinoma of Gleason score 6. Imaging techniques showed no metastatic lesions. He was treated by estrogen therapy. At 80 years, he consulted our hospital because of erythematous patch in the trunk. Biopsy showed mild infiltrations of lymphocyte and eosinophils. The lesion disappeared spontaneously. At 82 years, he consulted our hospital of because of erythematous patch at the back, and biopsy showed mildly atypical lymphocytes positive for CD20 and CD45, but negative for CD30, CD45RO, S100 protein, and cytokeratin (CK). Lymphoma was suspected but not definite. The lesions spontaneously disappeared. At 86 ages, he also consulted our hospital because of plaques in the face. Biopsy showed proliferation of atypical lymphocytes, marked infiltration of mature eosinophils, marked infiltration of these cells in the fair follicles (folliculotropism), and poorly differentiated invasive SCC arising from follicular cells. An immunohistochemical analysis showed that the atypical lymphocytes are T-lymphoma cells with T-cell markers, cyclinD1, p53, and high Ki67 labeling (50%) but without B-cell markers, NK-cell markers and plasma cell markers. The eosinophils were mature, and lacked p53 and showed low Ki67 labeling (4%). The carcinoma was positive for CK, p53, cyclinD1, and high Ki67 labeling (35%). A diagnosis of MF in the plaque stage with marked non-neoplastic eosinophilic infiltration, marked folliculotropism, and coexistent poorly differentiated invasive SCC was made by the author. Post-biopsy imaging techniques showed no metastasis or lymphadenopathy in the body. The patient was now treated by chemotherapy.