Hodgkin's Lymphoma in the Portuguese Population – Epidemiological and Pathological Characterization.
Authors: Silva Maria Gomes , Esteves Susana , Barbosa Inês , Cabeçadas José 
Published: October 2019

Abstract
Abstract 4634
Classical Hodgkin's lymphoma (cHL) has a bi-modal age distribution in the Western World, with a peak in young adults and another over 50 yo. The nodular sclerosis subtype predominates, mainly in the first group. In contrast, in developing countries, higher incidences in childhood and elderly populations and a predominance of the mixed cellularity subtype is observed. The epidemiological characteristics of the disease in Portugal, an European country with an elevated number of immigrants from West Africa, have not been reported. We aimed to determine the histological distribution and sex and age-specific incidence of Hodgkin's lymphoma in the Portuguese population and compare it to the Western pattern. For that, we performed a retrospective analysis of all cases registered at the Portuguese Cancer Registry-South Region (a network comprising 29 hospitals representative of the country's epidemiology) between 1999 and 2003 and determined the sex and age-specific incidence (cases/100 000 inhabitants) and exact 95% confidence intervals. Population data was obtained from the National Institute of Statistics. To investigate a possible recent trend for higher incidences in older ages, as has been described in other western countries, we used the Standardized Incidence Ratio (SIR) for comparison between 2006-2007 and 1999-2000. A total of 615 cases were diagnosed in the south of Portugal between 1999 and 2003, with a male/female ratio of 1.24:1. The age specific incidence revealed a bi-modal distribution with a peak at 15-24 yo (4.41/100 000 inhabitants) and another at 65-74 yo (2.94/100 000/inhabitants). The incidence of the disease in individuals older than 55 in 1999-2000 and 2006-2007 (3.56 and 3.81 in men, respectively, and 1.89 and 2.87 in women, respectively) increased by 25% (SIR:1.25, 95% CI:1.02-1.52, p=0.03 two-sided Mid-P exact test). This was mainly attributable to an increased incidence in women older than 55 (SIR:1.50; 95% CI:1.12-1.99, p=0.007), whereas in men the incidence remained stable (SIR:1.07, 95% CI:0.80-1.41, p=0.60). Since the registry data did not include histology in 27% cases, we systematically reviewed the pathological specimens of 229 consecutive patients diagnosed in our tertiary cancer care center during the same period (1999-2003). These patients were younger than the ones diagnosed in the other network hospitals (median age 29 and 40.5 yo, respectively, p<0,001 Mann-Whitney test), with a similar male to female ratio. 92% were subclassifiable. From these, 5% had nodular lymphocyte predominance HL and 95% (199 cases) cHL. Nodular sclerosis accounted for 89% of cHD and mixed cellularity for 6.5% of cases. From the other 233 registry cases classified as cHD, 78% were also nodular sclerosis.
In Portugal, where immigration from African countries could have lead to different disease characteristics, epidemiological patterns of HL are similar to the Western ones. Similarly to reports from other western countries, we observed a trend for an increased incidence in the elderly. A higher than expected proportion of nodular sclerosis subtype was found in a subgroup analysis, which may be related to the younger age reported in this subgroup.

Disclosures:
No relevant conflicts of interest to declare.