Objective:

To investigate the association between medically assisted reproduction (MAR) and the risk of hormone-related cancers in women.

Approach:

• Study Design: A retrospective cohort study using an emulated target trial design based on linked Australian national registries and administrative datasets.
• Population: Included 1,748,927 women aged 18 to 55 years from 1991 to 2018, with 396,661 undergoing MAR.
• Treatment Exposure: Included assisted reproductive technology (ART), intrauterine insemination or ovarian stimulation (IUI/OS), and ovulation induction with clomiphene citrate.
• Outcomes: Main outcomes were incident hormone-related invasive cancers, including breast, ovarian, uterine, thyroid, colorectal, and melanoma.

Key Findings:

• Higher observed rates of hormone-related cancers were noted in women who underwent MAR, with hazard ratios ranging from 1.09 to 1.64, but these associations may be influenced by underlying infertility-related conditions and increased medical surveillance.
• The estimated excess risk amounted to fewer than 20 additional cancers per 100,000 treated women annually compared to matched groups.
• Increased risks were observed in the first years following MAR, decreasing over time, often reaching little or no excess risk after approximately 10 years.
• Underlying infertility-related conditions may account for several observed associations with cancers.
• Increased medical surveillance and earlier cancer detection may contribute to the observed associations.

Interpretation:

The findings indicate that the observed associations with hormone-related cancer following MAR may reflect underlying patient characteristics and increased medical surveillance rather than treatment effects.

Limitations:

• The observational design prevents establishing causality.
• Important confounders such as the underlying cause of infertility, smoking, family history of cancer, and other patient characteristics were unavailable.
• Findings may not be generalizable beyond Australia's subsidized MAR system.

Conclusion:

The study indicates that any excess risk of hormone-related cancer following MAR may be influenced by the health and sociodemographic profile of women receiving MAR and increased surveillance during treatment.

Sources:

• JAMA Network Open