What do moles have to say about breast cancer risk?

Women with a greater number of cutaneous nevi may be more likely to develop breast cancer than those with fewer, according to a recent study in PLoS Medicine.

Researchers from Indiana University, Harvard University, and INSERM in France used the Nurses’ Health Study to follow 74,523 female nurses for 24 years, from 1986 to 2010. They adjusted for known risk factors of breast cancer in the models. Over the course of the 24 years, 5483 cases of invasive breast cancer were diagnosed.

Women with more cutaneous nevi had higher risks of breast cancer when compared to women with no nevi (multivariable-adjusted hazard ratio, 1.04, 95% confidence interval [CI], 0.98–1.10 for 1–5 nevi; 1.15, 95% CI, 1.00–1.31 for 6–14 nevi, and 1.35, 95% CI, 1.04–1.74 for 15 or more nevi; P for continuous trend = 0.003). During the follow-up period, women with no cutaneous nevi had an absolute risk of 8.48%; women with 1 to 5 nevi had an absolute risk of 8.82% (95% CI, 8.31%–9.33%); women with 6 to 14 nevi had an absolute risk of 9.75% (95% CI, 8.48%–11.11%); and women with 15 or more nevi had an absolute risk of 11.4% (95% CI, 8.82%–14.76%). The increased risk of breast cancer associated with cutaneous nevi was only seen with estrogen receptor (ER)-positive tumors (multivariable-adjusted hazard ratio per five nevi, 1.09, 95% CI, 1.02–1.16 for ER+/progesterone receptor [PR]–positive tumors; 1.08, 95% CI, 0.94–1.24 for ER+/PR− tumors; and 0.99, 95% CI, 0.86–1.15 for ER−/PR− tumors).

The researchers also tested plasma hormone levels among a subgroup of postmenopausal women who had not used postmenopausal hormones (n = 611). When compared to postmenopausal women with no nevi, postmenopausal women with 6 or more nevi had a 45.5% higher level of free estradiol and a 47.4% higher level of free testosterone (P for trend = 0.001 for both). In another subgroup of 362 breast cancer cases and 611 matched controls with plasma hormone measurements, the multivariable-adjusted odds ratio for every 5 nevi attenuated from 1.25 (95% CI, 0.89–1.74) to 1.16 (95% CI, 0.83–1.64), after adjustment for plasma hormone levels.

The investigators concluded that cutaneous nevi appear to affect plasma hormone levels and can signal breast cancer risk, independent of previously known factors. However, they do point out that the number of nevi were self-counted and that the study only looked at white women.

To get weekly advice for today's Ob/Gyn, subscribe to the Contemporary Ob/Gyn Special Delivery.