Morphologic appearance of regression in thin cutaneous melanomas Sabina Zurac 1, R. Andrei 1, T. Tebeica 1, Roxana Mustata 2, Gabriela Negroiu 3, Stefana Petrescu 3, Virginia Chitu 4, Rozalia Olsavszky 4, A. Rebosapca 5, B. Andreescu 5, I. Marinescu 5, Florica Staniceanu 1 1.Dept. of Pathology, 4.Dept. of Dermatology, 5.Dept. of Plastic Surgery Colentina University Hospital, 2.Terramed Conformal Clinic, 3.Institute of Biochemistry of Romanian Academy, Bucharest, Romania Sabina Zurac 1, R. Andrei 1, T. Tebeica 1, Roxana Mustata 2, Gabriela Negroiu 3, Stefana Petrescu 3, Virginia Chitu 4, Rozalia Olsavszky 4, A. Rebosapca 5, B. Andreescu 5, I. Marinescu 5, Florica Staniceanu 1 1.Dept. of Pathology, 4.Dept. of Dermatology, 5.Dept. of Plastic Surgery Colentina University Hospital, 2.Terramed Conformal Clinic, 3.Institute of Biochemistry of Romanian Academy, Bucharest, Romania Background: Regression in melanoma is a relatively common phenomenon, occurring in 10-35% of cases, depending on stage (up to 60% of melanoma thinner than 0.75 mm). However, despite accumulated data indicating both tumor regression achievement by immune cell action on tumor cells and crucial significance of the immune response in malignancies of other organs, the biologic significance of regression in melanomas is still on debate. Material and method: We analyzed 46 thin superficial spreading melanomas (Breslow index < 1mm): -25 presented regression (14 with segmental regression - SR, 11 with partial regression PR) -21 cases had no regression (NR). Material and method: We analyzed 46 thin superficial spreading melanomas (Breslow index < 1mm): -25 presented regression (14 with segmental regression - SR, 11 with partial regression PR) -21 cases had no regression (NR). Results:  PR melanoma predominates in yrs patients  SR melanoma mainly in yrs patients (P=0.0198).  PR melanoma predominates in yrs patients  SR melanoma mainly in yrs patients (P=0.0198).  Slight tendency towards spindle cell phenotype in NR melanomas.

 Regression absent in melanomas with high mitotic index (P=0.029) with tendency towards fewer mitoses in SR than PR and/or NR melanomas.  Very thin melanomas (Breslow <0.45 mm) tends to associate PR.  SR melanomas tend to have larger regression areas with lesser fibroplasia than PR cases. Partial regression in melanoma with Breslow Partial regression in melanoma without noticeable mitoses. Partial regression with moderate fibrosis in the regressed area.

 Tumor infiltrating lymphocytes (TIL) are almost significantly more numerous in SR melanomas than NR ones (P=0.06), while PR and NR melanomas have similar TIL distribution.  The more extended, the thicker were the areas of regression in SR melanomas.  SR melanomas associate presence of plasma cells within tumor inflammatory infiltrate (P=0.0173), while PR melanomas do not (P=0.21). Relatively frequent TILs in melanoma with segmental regression in other areas Plasma cells in segmental regression

Conclusions: In thin melanomas, partial and segmental regression seem to belong to different spectrum of alteration. SR melanomas present features usually associated with better prognosis (older age, low mitotic index, TIL presence) There are significantly more numerous plasma cells within SR areas, suggesting an antibodies-mediated immunological mechanism rather than a cellular one as previously expected. Conclusions: In thin melanomas, partial and segmental regression seem to belong to different spectrum of alteration. SR melanomas present features usually associated with better prognosis (older age, low mitotic index, TIL presence) There are significantly more numerous plasma cells within SR areas, suggesting an antibodies-mediated immunological mechanism rather than a cellular one as previously expected. Acknowledgments: project partially supported by Postdoctoral Program POSDRU/89/1.5/S/60746 Extended area of segmental regression