Classical Hodgkin lymphoma (cHL) belongs to the most curable lymphomas in adults. Some cHL however, are primary refractory to usual treatments including anthracyclins regimen. Currently, only clinical factors are considered as relevant for prognosis. In a previous study of a small cohort of patients, we showed that some immunohistochemical markers could help for predicting the treatment response of cHL. In this study, we extended the markers and increased the number of included patients. We performed a retrospective study on pre-treatment biopsy specimen of 59 patients, 18 with primary refractory cHL and 41 responders to chemotherapy and free of disease for at least 3 years. Most refractory cHL had a nodular sclerosis (NS) histological type, except one which was a mixed cellularity type. Thirty six responders had a NS type, 3 patients had a mixed cellularity type and the 2 others an interfollicular cHL. The semi-quantitative immunohistochemical study used CD20, CD3, CD30, bcl2, p53, Ki67, TiA1 and c-kit antibodies. The results were statistically evaluated using a Fisher ’s exact test or a Wilcoxon sum rank test depending on the variable studied. CD30 and Ki67 stained strongly Hodgkin (Hg) and Reed-Sternberg (RS) cells regarless the response status. In contrast, these cells expressed significantly less frequently CD20 in refractory cHL than in responders (p= 0.032) and were never stained with CD3. P53 and bcl2 had a significantly higher expression on Hg or RS cells in refractory cHL (median = 63% & 51%) compared to responders (median = 40% & 12%) (p=0.004 & p=0.015 respectively). The cytotoxic marker TiA1 stained significant higher number of small lymphocytes in refractory cHL (median=42.5 per high power field (hpf)) compared to responders (median= 21 per hpf) (p= 0.0006). C-kit antibody was negative in Hg or RS cells but stained significant more mastocytes in refractory cHL (median=9 per hpf) comparing to responders (median=3.8 per hpf) (p= 0.001). These results indicate that immunohistochemical markers are useful in cHL and should be used in association with clinical parameters for predict the cHL treatment response. The prognostic significance of CD20 expression in cHL is controversial but in this study seems predictive of a better treatment response and is merely a marker of different gene expression program that may be associated with a more favorable outcome. A high bcl2 and p53 expression in refractory cHL supports the notion that an intact apoptosis cascade is essential for cell killing effect of chemotherapy. The increasing of TiA1 and c-kit positive cells raises the importance of the environmental non-neoplastic cells in cHL and suggests that targeted therapy against mast cells could improve prognosis of refractory cHL.

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