Mortality risk from pregnancy-associated cancers

Overall 5-year mortality is at an increased risk in patients diagnosed with pregnancy-associated cancers, according to a recent study.

Pregnancy-associated cancer is estimated to occur in 1 in 1000 pregnancies, with an increase in incidence observed over time. Only 25% of pregnancy-associated cancers are diagnosed during pregnancy, with most diagnosed in the postpartum period.

Increased mortality has been associated with pregnancy-associated breast cancer, but long-term outcomes of other cancers are not well known. Investigators conducted a study to determine long-term mortality in women with pregnancy-associated cancers and compared this data with cancers not associated with pregnancy.

Administrative data was gathered from 3 provinces in Canada: Alberta, British Columbia (BC), and Ontario. Data from Alberta was contained in Alberta Health Services, and data from BC was assessed using Population Data BC and Ontario using the Institute for Clinical and Evaluative Sciences. Cancer was identified in women using cancer registries in the provinces.

Patients with cancer diagnoses from January 1, 2003, to December 31, 2016, were included in the analysis. Follow-up continued through December 31, 2017, or death, leading to 1 to 14 years of follow-up for patients depending on date of diagnosis and death.

Excluded cancers included stage 0 cancers, nonmelanoma skin cancers, squamous intraepithelial neoplasia grade 3, and high-grade squamous intraepithelial cervix lesions. 

There were 3 cohorts in the study: women diagnosed with cancer during pregnancy, women diagnosed with cancer postpartum, and women diagnosed with cancer outside of pregnancy. The first diagnosis of cancer was used for women with multiple diagnoses.

Overall survival at 1 year and 5 years and time from cancer diagnosis to death from any cause were measured as the primary outcomes of the study. Covariates included cancer stage, cancer site, age at cancer diagnosis, and days between diagnosis and first treatment.

Of the 23,307 participants, 1014 were diagnosed with cancer during pregnancy, 3074 postpartum, and 20,219 outside of pregnancy. Participants were diagnosed during pregnancy at a mean 31.9 years, postpartum a mean 32.6 years, and outside of pregnancy a mean 36.5 years.

At delivery, the gestational age was about 37 weeks for individuals diagnosed during pregnancy, and 38.5 weeks for those diagnosed postpartum. The preterm birth rate in these groups was 32% and 10% respectively. 

Women diagnosed during pregnancy and outside of pregnancy were most often diagnosed with breast cancer at 26% and 30% respectively, while those diagnosed postpartum were most often diagnosed with thyroid cancer at 24%.

While 1-year survival was consistent across all 3 groups, 5-year survival decreased in the pregnancy and postpartum diagnosis groups, at 87% in the pregnancy group, 89% in the postpartum group, and 93% in the outside pregnancy group. Both 1-year and 5-year survival were reduced in breast cancers associated with pregnancy.

Follow-up lasted a mean 6.3 years, with a 9% mortality rate. Mortality rates were overall greater in participants with pregnancy-associated cancers compared to non-pregnancy-associated cancers.

Reference

Cairncross ZF, Shack L, Nelson G, et al. Long-term mortality in individuals diagnosed with cancer during pregnancy or postpartum. JAMA Oncol. 2023. doi:10.1001/jamaoncol.2023.0339