Classic Hodgkin Lymphoma: the malignant cells and tumour microenvironment in adults of different ages
Buxton, Jennifer Katie
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Classic Hodgkin Lymphoma (cHL) has an annual incidence of 2.4 cases per 100 000 population in the UK, and is one of the most common malignancies diagnosed in young adults aged 15 to 34. The majority of younger patients have a good long-term outcome with between 80 and 90% disease-specific survival but cHL also affects older adults in whom the prognosis is significantly poorer. The role of tumour-associated macrophages (TAM) in cHL has gained much interest, with several studies reporting an association between high numbers of CD68-positive TAM and poor prognosis. There is also a question over the prognostic significance of Epstein-Barr Virus (EBV) infection which is implicated in up to 50% of cHL cases in developed countries. Published data suggests that EBV positivity in elderly patients may be associated with a poorer outcome, whereas in younger adults may be of prognostic benefit. Differences related to age are of interest particularly as an age-related decline in immunity has been linked with the development of certain subtypes of Non-Hodgkin Lymphoma in older patients. In a retrospective study, two separate cohorts of patients with cHL were examined with the aim of identifying: • Differences in the cellular composition of the tumour microenvironment in cHL which has arisen in young and elderly adult patients; • Differences in the cellular composition of the tumour microenvironment in cHL associated with or without EBV infection; • Factors within the tumour microenvironment which may influence prognosis and may be targeted for novel treatments. One group consisted of patients aged between 15 and 34 years at diagnosis and the other, of those aged 60 or over at presentation. Tissue obtained at the time of diagnosis was examined with regard to a number of factors related to the malignant cells and the surrounding microenvironment, including the number and phenotype of macrophages, the number of plasmacytoid dendritic cells and the number of malignant Hodgkin Reed-Sternberg (HRS) cells and non-malignant ‘background’ cells undergoing apoptosis. Comparisons were made between the two age groups, also taking into account the EBV-status of tumours, cHL subtype and gender. Results confirmed the current understanding that EBV-positive cHL is more common in older patients and has a strong, but not exclusive, association with the MCHL subtype. In addition, a strong link between young males and EBV-positive disease was shown. Macrophages were found to vary between the two age groups, in number and phenotype and there were clear differences associated with the presence or absence of EBV infection. While no definite link with outcome and macrophages was identified it was apparent that the implications of macrophages in the tumour microenvironment may differ between the two age groups. The number of apoptotic cells correlated closely with the number of macrophages and in the young the number of HRS cells was associated with prognosis. Investigation of the tumour microenvironment is complex and caution is needed in interpreting studies which do not differentiate between patients according to age, as tumour characteristics may have variable implications in different age groups. In this thesis a number of clinicopathological differences were identified between the two age groups. These point to the need for further larger studies to delineate how such age-related differences may or may not be associated with immune function and how this information could be translated into treatments to improve outcomes.