Mathematical analysis of the effect of in utero exposure on cancer in female B6C3F1 mice using mortality data

PURPOSE: Using experimental data from the lifespan study conducted at the Institute for Environmental Sciences on female B6C3F1 mice exposed in utero, the effect of radiation exposure in utero on cancer was analyzed using a mathematical model focusing on the effect of radiation on the occurrence of cancer; progression of cancer over time; and death due to cancer. MATERIALS AND METHODS: Data used for analysis were extracted from the in utero lifespan experiment (non-irradiated controls and irradiated group, 400 mGy/day x18 days) including: age at death, cause of death, and neoplasm(s) observed at the time of death. The new method based on our mathematical model, was introduced to evaluate the temporal change in the cancer incidence rate and focused on competing risks between different cancers such as malignant lymphomas and solid cancers. To validate the new method, we compared it to our previous analysis. RESULTS AND CONCLUSIONS: The analysis showed that in utero exposure shortened the mean life expectancy due to solid cancer by 199.4 days whereas that of malignant lymphoma was not significantly affected by the exposure. There was also no change in the mean age at occurrence and progression (time between occurrence until it caused death) for malignant lymphomas. For solid cancers, the mean age at the occurrence was shortened by 185.7 days whereas the progression period remained unchanged.