Three comprehensive Swedish studies have revealed new insights into the complex relationship between cancer and pregnancy, highlighting both increasing incidence rates and relatively favorable outcomes for certain cancer types.
The analysis of Swedish birth and cancer registers from 1973 to 2017 shows a significant upward trend in pregnancy-associated cancer (PAC) rates. The incidence increased from 21.3 per 100,000 pregnancies in 1980-1984 to 38.2 per 100,000 in 2010-2014. Age emerged as a crucial factor, with rates ranging from 5.3 cases per 100,000 in women aged 15-19 to 63.5 cases per 100,000 in those aged 40-44.
Risk Factors and Demographic Patterns
The studies identified several significant risk factors for pregnancy-associated cancer. Smoking showed a notable correlation with increased cancer risk (IRR 1.28; 95% CI, 1.07-1.54), particularly for cervical cancer where the risk more than doubled (IRR 2.32; 95% CI, 1.52-3.54). Conversely, immigrant background was associated with lower overall cancer rates (IRR 0.76; 95% CI, 0.64-0.91).
Breast Cancer Outcomes and Pregnancy Impact
A focused analysis of breast cancer cases revealed encouraging findings regarding maternal outcomes. Despite higher rates of planned preterm deliveries (42.6%) and cesarean sections, women with breast cancer during pregnancy did not show increased risks for major pregnancy complications. Notably, none of the pregnant women with breast cancer experienced gestational diabetes, pre-eclampsia, or stillbirth.
Timing and Tumor Characteristics
The timing of breast cancer diagnosis during pregnancy appeared to influence tumor characteristics and outcomes. Third-trimester diagnoses showed more aggressive features, including:
- Larger tumor sizes
- Higher rates of distant metastases
- Increased likelihood of ER-negative status (54% vs 32% in non-pregnant cases)
- Greater prevalence of HER2-positive tumors (22% vs 9%)
Mortality rates varied significantly by trimester of diagnosis. While first-trimester cases showed comparable mortality rates to non-pregnant cases (18.6 vs 19.1 per 1000 person-years), second and third-trimester diagnoses were associated with higher mortality rates of 42.0 and 37.1 per 1000 person-years, respectively.
Preterm Delivery Patterns
The research highlighted a significant disparity in preterm delivery rates between women with PAC during pregnancy (30.6%) compared to the general population (5.3%). For those diagnosed with cancer within one year following delivery, the preterm rate was 8.1%, suggesting that active cancer during pregnancy has a more substantial impact on delivery timing.
