Identification of aspartame-induced haematopoietic and lymphoid tumours in rats after lifetime treatment

•Immunohistochemistry (IHC) is an essential tool to confirm and characterize the neoplastic origin of a lesion.•A review of the haematopoietic and lymphoid tissue tumours (HLTs) from the prenatal long-term APM study in rats was performed.•The leukaemogenic and lymphomatogenic effect of APM was confirmed following IHC characterization of HLTs. Lymphomas and leukaemias involving the lung have in some cases been hard to distinguish from respiratory tract infection in Sprague-Dawley (SD) rats from long-term bioassays. In order to differentiate between tumours and immune cell infiltrates, updated pathological criteria and nomenclature were used and immunohistochemistry (IHC) was applied to haematopoietic and lymphoid tissue tumours (HLTs) in the original prenatal long-term Aspartame (APM) study performed by the Ramazzini Institute (RI). All 78 cases of HLTs from treated and control groups were re-examined based on light microscopic morphological characteristics and subjected to a panel of IHC markers including Ki67, CD3, PAX5, CD20, CD68, TdT, CD45, CD14 and CD33. The analysis confirmed the diagnoses of HLTs in 72 cases, identified 3 cases of preneoplastic lesions (lymphoid hyperplasia), and categorized 3 cases as inflammatory lesions. A statistically significant increase in total HLTs (p = 0.006), total lymphomas (p = 0.032) and total leukaemias (p = 0.031) in treated female rats was confirmed (high dose vs control), and a statistically significant linear trend for each HLT type was also observed. After the HLT cases re-evaluation, the results obtained are consistent with those reported in the previous RI publication and reinforce the hypothesis that APM has a leukaemogenic and lymphomatogenic effect.