Epidemiology and prognosis in classical Hodgkin lymphoma

Hollander, P. 2018. Epidemiology and prognosis in classical Hodgkin lymphoma. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine 1411. 70 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-513-0189-1. Classical Hodgkin lymphoma (HL) is a B cell derived neoplasm with an overall good prognosis. Its etiology and pathogenesis are largely unknown. The tumor microenvironment consists of sparse malignant cells and abundant leukocytes. In paper I we found that patients with rheumatoid arthritis (RA) had an increased risk of developing HL, especially patients with proxies of more severe RA. In addition, patients with RA had an especially increased risk of developing Epstein-Barr virus positive HL. These findings indicate that patients exposed to chronic inflammation have an increased risk of developing HL. We further studied the inflammatory milieu in the microenvironment of HL in paper II by investigating different leukocytes with immunohistochemical markers on diagnostic HL biopsies. We demonstrated that an anergic immune signature with a high amount of immune suppressive regulatory T lymphocytes was associated with inferior time to progression in an age-adjusted analysis. Another mechanism utilized by malignant cells and leukocytes to induce a suppressed antitumor immune response is to upregulate expression of programmed death ligands 1 and 2 (PD-L1 and PD-L2), that induces apoptosis in tumor killing leukocytes by binding to programmed death receptor 1 (PD-1). In paper III, we investigated the prognostic impact of PD-1, PD-L1 and PD-L2 in the tumor microenvironment of diagnostic HL biopsies with immunohistochemistry. We found that high proportions of PD-1+ and PD-L1+ leukocytes were associated with worse outcome in fully adjusted multivariate analyses. However, both PD-1 and PD-L1 are expressed to variable degrees in malignancies. Therefore, in paper IV we wanted to determine how expression of PD-1 and PD-L1 changes in repeated biopsies from both untreated and treated patients with relapsed HL. There were increased proportions of PD-1+ and PD-L1+ leukocytes, and PD-L1+ tumor cells in the relapse biopsies compared to the primary biopsies. These findings indicate that the PD-1 pathway is upregulated due to primary treatment, longer disease duration or altered conditions in the microenvironment at relapse.