Abstract: 【Abstract】 Objective To investigate clinicopathological features of hypopigmented mycosis fungoides（HMF） and hypopigmented interface T-cell dyscrasia （HITCD）. Methods A total of 41 patients with cutaneous hypopigmented lymphoproliferative diseases, who had complete clinicopathological data, were collected from Department of Dermatology, the Third People′s Hospital of Hangzhou from January 2015 to September 2020, and the clinicopathological and immunophenotypic features were analyzed. Comparisons of normally distributed measurement data were carried out using t test, comparisons of categorical data using Chi-square test or Fisher′s exact test, and comparisons of ranked data between 2 groups using rank-sum test. Results All of the 41 patients clinically presented with irregular hypopigmentation, some of which was accompanied by erythema or furfuraceous scales. In terms of pathological features, 21 patients showed infiltration and aggregation of atypical lymphoid cells in the epidermis, which was consistent with typical pathological features of mycosis fungoides, and they were diagnosed with HMF; 20 patients showed vacuolar degeneration of the basal layer, accompanied by infiltration of lymphoid cells and mild epidermotropism, and they were diagnosed with HITCD. All immune cells expressed T-cell phenotype, and epidermal lymphocytes expressed a CD8-dominated phenotype in 14 （67%） cases of HMF and 13 （65%） of HITCD. In the epidermis, the total number of lymphocytes was significantly higher in the HMF group than in the HITCD group （t = 1.81, P = 0.012）; in the dermis, the number of CD4+ lymphocytes and CD8+ lymphocytes, and the total number of lymphocytes were all significantly higher in the HMF group than in the HITCD group （t = 2.64, 1.51, 2.60, P = 0.012, 0.002, 0.001, respectively）. All patients were treated with narrow-band ultraviolet B radiation. Among 34 patients who completed the follow-up, 30 achieved complete clearance of skin lesions without recurrence, including all patients with HITCD, and 4 with HMF achieved partial regression of the lesions. Conclusions Compared with HMF, HITCD presents different pathological characteristics and benign biological behaviors. Thus, HITCD should be distinguished from HMF as an independent disease. Phototherapy alone is effective for the treatment of HITCD.

Key words: Mycosis fungoides, Hypopigmentation, Pathologic processes, Treatment outcome, Hypopigmented mycosis fungoides, Hypopigmented interface T-cell dyscrasia