Cancer Treatment During Pregnancy and Maternal and Infant Outcomes: A Descriptive Cohort Study Using a Japanese Claims Database

PURPOSE: To characterize cancer treatment during pregnancy and maternal and infant outcomes among women with cancer identified during pregnancy in Japan. METHODS: In this descriptive cohort study, we used mother-infant linkage data from the JMDC claims database from 2005 to 2024. Live-birth pregnancies were considered eligible when a malignant neoplasm (ICD-10 C00-C97) was recorded between the estimated pregnancy onset and delivery. Exposure was defined as at least one anticancer agent prescribed between the diagnosis and delivery; surgery and radiation therapy were also identified. The outcomes were preterm delivery and major congenital malformation at 6 months of age. Pregnancies without a diagnosis of malignant neoplasms constituted the internal reference group. RESULTS: Of the 500 pregnancies with cancer identified during pregnancy, 16 (3.2%) had an anticancer agent prescribed, 46 (9.2%) underwent surgery for malignant tumors, and none underwent radiation therapy. Cancer was identified in the second trimester in 10 of the 16 pregnancies with exposure (62.5%) and in 128 of the 484 pregnancies without exposure (26.4%). All eight pregnancies with breast cancer received an anthracycline with cyclophosphamide. The frequencies in the reference group (n = 236 002), without exposure, and with exposure were 12.0%, 20.9%, and 37.5% for preterm delivery and 6.1%, 9.1%, and 12.5% for major congenital malformation, respectively. CONCLUSIONS: Cancer identified during pregnancy was treated in a minority of women, and anticancer agents were most often prescribed when cancer was identified in the second trimester. Outcomes were recorded more often in pregnancies with cancer but cannot be attributed to anticancer agent exposure.