Breast cancer incidence in women with endometriosis

The risk of breast cancer in endometriosis?

Key Points

Highlight:

• Risk of breast cancer is increased in women less than 40-years of age with surgically verified endometriosis

Importance:

• The relationship between endometriosis and breast cancer is not known and shown to be either increased or similar in earlier studies.

What's done here?

• The authors assessed the risk of breast cancer in women with endometriosis.
• Women with surgically confirmed endometriosis (n=49,933) were identified from the Finnish Hospital Discharge Registry in Finland.
• Breast cancer diagnosis after endometriosis was identified.
• Factors examined were the age at cancer diagnosis, time from endometriosis diagnosis, the type of endometriosis being peritoneal, deep, ovarian endometriosis; and breast cancer histology.
• The standardized incidence ratio (SIR) of breast cancer was calculated for the whole cohort.

Data:

• Overall breast cancer risk is similar to the rest of the population.
• However, breast cancer in 20-39 years is increased.
• The risk of in situ breast cancer is also higher in endometriosis, compared to the general population.

Limitation:

• There were potential confounding factors, which include
  • the decreased parity or late first pregnancy among women with endometriosis may increase breast cancer risk; 
  • the body mass index is decreased in women with endometriosis; and,
  • hormonal therapy usage.

Lay Summary

The relationship between endometriosis and breast cancer remains unclear. Some studies have shown an increased risk of breast cancer among women with endometriosis, while others suggested no change in the risk of breast cancer.

Previously, the authors have found that the overall risk of breast cancer in women with endometriosis was similar to the Finnish female population, irrespective of the type of endometriosis. However, the authors have re-examined the potential risk because breast cancer is one of the most common cancers in fertile-aged women. Thus, this study conducted by Saavalainen et al. from Department of Obstetrics and Gynecology, University of Helsinki, Finland investigated the risk of breast cancer according to the age at which breast cancer was diagnosed, time from endometriosis diagnosis as well as breast cancer histology (i.e. ductal and lobular) and separately for breast carcinoma in situ. The study outcome was published in Acta Obstetricia et Gynecologica Scandinavica.

Women with surgically confirmed endometriosis (n=49,933) during 1987-2012 were retrieved from the Finnish Hospital Discharge Register in Finland. The breast cancers diagnosed afterwards were identified from the Finnish Cancer Registry. The reference point was the Finnish female population. The study measurement was standardized incidence ratio (SIR) of breast cancer in the whole cohort, in subtypes of endometriosis, and stratified by the age at breast cancer diagnosis, histology, and time from endometriosis diagnosis.

The results show that women with endometriosis do not have an overall increased risk of breast cancer. This is irrespective of the type of endometriosis.  However, the risk of ductal and lobular breast cancer did not differ, but an increased incidence of breast cancer among the 20-39 -year-olds was observed. The incidence of in situ of the breast carcinoma was increased.

While a positive risk was shown, it must be noted that the study may be confounded with other possible risk factors for breast cancer in young women, which include low body mass index and oral contraceptives usage.

Research Source: https://www.ncbi.nlm.nih.gov/pubmed/30883685