Histological analyses of the Ishii (1981) rat carcinogenicity study of aspartame and comparison with the Ramazzini Institute studies

Researchers from the Ramazzini Institute have reported that lifespan dosing of rats with aspartame treatment is associated with an increased overall incidence of malignant tumors, including leukemias/lymphomas, transitional cell carcinomas of the renal pelvis/ureter, and malignant schwannomas of the peripheral nerves. Other carcinogenicity studies conducted on aspartame have shown no such carcinogenic potential in any organ system. Additional data to assess the carcinogenic potential of aspartame, especially in relation to the publications of the Ramazzini Institute, were obtained from a third-party histological evaluation of tissues from a carcinogenicity study previously conducted to assess the potential for aspartame to induce tumors of the brain. The results of this histological evaluation provide no evidence of a tumorigenic effect of aspartame in any organ group, including those organs/tissues reportedly affected in the Ramazzini Institute's studies. The only effects identified were an increased incidence of renal pelvic mineralization and renal pelvic hyperplasia secondary to the irritant properties of the mineralization process. The toxicological significance of these particular findings is widely considered minimal. There is no evidence that aspartame is carcinogenic in rats, at least to doses of 4 g/kg body weight/day administered over a 2-year period.