TOPLINE:

Women diagnosed with endometriosis or adenomyosis had elevated risks for breast and gynaecological cancers compared with those without these conditions, with strong associations observed within the same calendar year as diagnosis.

METHODOLOGY:

• Researchers in Sweden conducted a nationwide cohort study to evaluate the short-term and long-term associations between endometriosis or adenomyosis and the risk for specific gynaecological and breast cancers in women.
• They included 49,133 women (mean age, 42.7 years) diagnosed with endometriosis or adenomyosis between 1997 and 2018, with a total mean follow-up duration of 20.2 years.
• Data on diagnoses of endometriosis or adenomyosis were obtained from the National Patient Register, whereas data on diagnoses of gynaecological and breast cancers were ascertained from the National Cancer Register.

TAKEAWAY:

• Overall, 3.6% of women were diagnosed with gynaecological or breast cancers, and the standardised incidence ratio (SIR) was 1.4 (95% CI, 1.3-1.5) among women with endometriosis or adenomyosis vs those without these conditions.
• Incidences of overall gynaecological or breast cancers were higher during the same calendar year as the diagnosis of endometriosis or adenomyosis (SIR, 9.4; 95% CI, 8.5-10.4), particularly for endometrial cancer (SIR, 47.0; 95% CI, 39.9-55.0) and epithelial ovarian cancer (SIR, 36.2; 95% CI, 29.2-44.4).
• Among patients with cancers diagnosed in subsequent calendar years after the diagnosis of endometriosis or adenomyosis, the risk remained elevated for epithelial ovarian cancer (SIR, 1.9) and breast cancer (SIR, 1.2).

IN PRACTICE:

"These findings indicate that clinicians should have a higher index of suspicion for gynecological or breast cancers in women diagnosed with endometriosis," the authors wrote.

SOURCE:

This study was led by Louise Moberg, Department of Gynaecology and Obstetrics, Skåne University Hospital, Lund University, Lund, Sweden. It was published online on May 14, 2026, in Acta Obstetricia et Gynecologica Scandinavica.

LIMITATIONS:

Detection bias could not be excluded because women with persistent symptoms often undergo diagnostic procedures that may lead to earlier cancer detection. The study's observational design precluded establishing causal inference. Women diagnosed with endometriosis or adenomyosis before the study period and those with prior removal of a gynaecological organ or a diagnosis of cancer were not excluded.

DISCLOSURES:

This study received support through non-commercial research grants. The authors declared having no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.