Apoptosis in CD30‐positive lymphoproliferative disorders of the skin

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Abstract
The spectrum of CD30-positive cutaneous lymphoproliferative disorders (CD30+ CLPD) includes lymphomatoid papulosis (LyP), primary cutaneous CD30+ large T-cell lymphoma (LTCL) and rare borderline patients. Despite their malignant histopathology, CD30+ CLPD exhibit a low-grade malignant course with an excellent prognosis and a characteristic tendency for spontaneous regression. Apoptosis of tumour cells is considered a principal mechanism of tumour regression. We examined the proliferation and apoptosis rates as well as the expression of apoptosis-related proteins in various clinical entities, tumour cell lines and evolutional (evolving and regressing) stages of CD30+ CLPD. Skin biopsies of LyP (n = 20) and LTCL (n = 19) and five CD30+ lymphoma cell lines were analysed by means of immunohistochemistry and Western blotting in order to evaluate the proliferation (Ki67), apoptosis (FragEl) and expression of Bax, Bcl-x, C-kit and Mcl-1. A significantly higher apoptotic index (AI) was found in LyP (AI = 12.5%) than in LTCL (AI = 3.1%, P < 0.005). Bax was expressed by the majority of tumour cells in all forms of CD30+ CLPD and CD30+ cell lines. However, no Bax expression was found in tumour cell lines derived from systemic CD30+ lymphomas, which lack spontaneous regression and display an aggressive clinical course. No significant correlation was found between the expression of apoptosis-related proteins and the tumour type and evolutional stage of CD30+ CLPD. We conclude that the higher AI in LyP may contribute to the regression of LyP lesions and the excellent prognosis of the disease. Pro-apoptotic protein Bax is expressed at high levels in CD30+ CLPD and may play a crucial role in mediating apoptosis of tumour cells