423 Analele Universităţii din Oradea, Fascicula Protectia Mediului Vol. XXV 2015 MALIGNANT CUTANEOUS SQUAMOMELANOCYTIC TUMOR, DIFFERENTIAL DIAGNOSIS ISSUE AND PECULIAR PERITUMORAL IMMUNE RESPONSE-CASE REPORT Pascalau Andrei, Mircea Sandor, Vilceanu Narcis , Ovidiu Pop ⃰ Marghita City Hospital, Marghita, strada Eroilor, nr. 12-14, Romania, pascalau_andrei@yahoo.com ⃰ ⃰University of Oradea- Faculty of Medicine and Pharmacy, Pta 1 Decembrie, nr 10, Oradea, Romania, drims75@yahoo.com, forensicanv@yahoo.com, drovipop@yahoo.com Abstract In the last decade there has been a real interest in the scientific community in understanding regarding the existence of mixed tumor cell populations what long had been and still are viewed with different points of embryological development. In this sense, the study of this relationship provided by melanocytes and keratinocytes and neoplasia is intriguing and still raise many questions and many difficulties of histological diagnosis; meantime difficulties of treatment ad poor prognostic understanding . In this paper we present the case rapport of 66-year-old patient, who had presented two synchronous tumors at the level of the left ear. These tumors were basal cell carcinoma and a special tumor type named squamo-malanocytic tumor. Immunohistochemistry methods managed to got a precise diagnosis using reactions for citokeratine, S100 and HMB45. The case presents a particularity of peritumoral immune response by this many CD4 lymphocytes Treg expressing CD25. These are lymphocyte subpopulations involved in mechanism of carcinogenesis. Key words: skin cancer, HMB45, S100,Treg, CD25, CD4 INTRODUCTION Between keratinocyte and melanocyte there is normally a close anatomical and functional relationship. In an attempt to explain this relationship have mentioned several hypotheses. One of these is the theory of "collision tumor ". This theory refers to the presence of two malignant tumors, one with melanocytic origin (melanoma) and the other with keratinocytic origin (basal cell carcinoma or squamous cell) which are located very close and inevitably "collide". Another theory is the theory that sad that basal cell carcinoma or squamous cell carcinoma are invaded by non-neoplastic melanocytes, containing abundant pigment (melanin), a phenomenon much more commonly encountered in the proliferation of skin benign lesion, such as Seborrheic keratoses. A third theory refers to the metastasis of melanoma "in transit", when it reaches a squamous cell carcinoma or a basal cell carcinoma. Malignant cutaneous tumor basomelanocytic or squamoumelanocyic is a lesion that