Multicenter phase II trial of temozolomide in mycosis fungoides/ sézary syndrome: Correlation with O ⁶-methylguanine-DNA methyltransferase and mismatch repair proteins

Purpose: Temozolomide (TMZ) is an oral derivative of dacarbazine that induces DNA damage by methylating nucleotide bases. Resistance has been associated with high levels of O ⁶-methylguanine-DNA methyltransferase (MGMT). Malignant CD4 ⁺ T cells of patients with mycosis fungoides/Sézary syndrome (MF/SS) have been shown to have low levels of MGMT and may be particularly sensitive to this methylator. Experimental Design: The efficacy of TMZ was evaluated in a multicenter phase II trial of patients with advanced stages of MF/SS. TMZ was given orally at daily doses of 200 mg/m ² for 5 days every 28 days. MGMT and mismatch repair protein expression was assessed by quantitative immunofluorescence and immunohistochemistry in skin and blood samples. Results: Twenty-six patients (stages IB-IVB) were evaluable for response. Patients had a median of four prior treatments. Median follow-up time was 19 months (range, 1-95). The overall response was 27% with two complete remissions (8%) and five partial remissions (19%). Median disease-free survival was 4 months. The median overall survival was 24 months. The most frequent toxicities included constitutional symptoms, gastrointestinal symptoms, and hematologic toxicities. Treatment was discontinued in three patients following grade 3 thrombocytopenia, lymphopenia, and skin reaction. The relationship between pretreatment MGMT and mutL homolog 1 (MLH1)/mutS homolog 2 (MSH2) mismatch repair protein expression levels in skin biopsies of cutaneous lesions and clinical response to TMZ were evaluated. Conclusions: Pretreatment levels of MGMT and MLH1/MSH2 protein levels are not predictive of response to TMZ in MF/SS, suggesting that other resistance mechanisms are important.