Serum calcium, tumor size, and hormone receptor status in women with untreated breast cancer.

Elevated serum levels of calcium are frequently observed in advanced breast cancer, but data on serum calcium and breast cancer characteristics at the time of breast cancer diagnosis are limited. We conducted a cross-sectional study of 555 women with newly-diagnosed, untreated breast cancer in North Dakota. We examined the relationship between tumor size, serum calcium and other clinical characteristics of breast tumors, including age and hormone receptor status, using multiple linear regressions. Tumors that were estrogen receptor negative tended to be associated with higher serum calcium levels (p = 0.07). We observed a significant positive correlation between tumor volume and serum calcium levels (adjusted for patient age, body mass index, hormonal receptors, stage at diagnosis, and grade). The association between tumor volume and serum calcium was limited to post-menopausal women. Our finding that postmenopausal women with larger breast tumors had significantly higher serum calcium levels is consistent with a calciotropic effect of early breast cancer in postmenopausal women.