Research published in the BMJ found no increased risk for uterine cancer or invasive breast cancer after assisted reproduction.
In the study of 255,786 British women, small increased risks for noninvasive breast and ovarian tumours were found, but the researchers say these results may not be because of the treatment itself and require further investigation.
The population-based, data linkage cohort study examined data for all women who underwent assisted reproduction in Great Britain between 1991 and 2010, as recorded by the Human Fertilisation and Embryology Authority.
Analysis found no significant increased risk for corpus uteri cancer (standardised incidence ratios [SIRs] 1.12; 95% CI, 0.95-1.30) during an average of 8.8 years of follow-up.
Overall, there was no significantly increased risk for breast cancer (SIR, 0.98; 95% CI, 0.94-1.01) or invasive breast cancer (SIR, 0.96; 95% CI, 0.92-1.00). An increased risk for in situ breast cancer was observed (SIR, 1.15; 95% CI, 1.02-1.29; absolute excess risk (AER) 1.7 cases/100,000 person-years [PYs]; 95% CI, 0.2-3.2) and was associated with an increasing number of treatment cycles (P=.03).
There was an increased risk for ovarian cancer (SIR, 1.39; 95% CI, 1.26-1.53; AER, 5.0 cases/100,000 PYs; 95% CI, 3.3-6.9). This increase was seen for both invasive (SIR, 1.40; 95% CI, 1.24-1.58; AER, 3.4 cases/100,000 PYs; 95% CI, 2.0-4.9) and borderline (SIR, 1.36; 95% CI, 1.15-1.60; AER, 1.7 cases/100,000 PYs; 95% CI, 0.7-2.8). Increased risks for ovarian tumours were limited to women with endometriosis, low parity or both.
The study authors suggest the increased risk for ovarian tumour could be because of patient characteristics, rather than assisted reproduction itself, although they point out that both surveillance bias and the effect of treatment are also the possibilities.