The prognostic significance of breast tumour microcalcifications

Deposition of calcium in an in vitro model of human breast tumour calcification reveals functional role for ALP activity, altered expression of osteogenic genes and dysregulation of the TRPM7 ion channel

Microcalcifications are vital mammographic indicators contributing to the early detection of up to 50% of non-palpable tumours and may also be valuable as prognostic markers. However, the precise mechanism by which they form remains incompletely understood. Following development of an in vitro model using human breast cancer cells lines cultured with a combination of mineralisation-promoting reagents, analysis of calcium deposition, alkaline phosphatase (ALP) activity and changes in expression of key genes was used to monitor the calcification process. Two cell lines were identified as successfully mineralising in vitro, MDA-MB-231 and SKBR3. Mineralising cell lines displayed higher levels of ALP activity that was further increased by addition of mineralisation promoting media. qPCR analysis revealed changes in expression of both pro- (RUNX2) and anti- (MGP, ENPP1) mineralisation genes. Mineralisation was suppressed by chelation of intracellular Ca2+ and inhibition of TRPM7, demonstrating a functional role for the channel in formation of microcalcifications. Increased Mg2+ was also found to effectively reduce calcium deposition. These results expand the number of human breast cancer cell lines with a demonstrated in vitro mineralisation capability, provide further evidence for the role of an active, cellular process of microcalcification formation and demonstrate for the first time a role for TRPM7 mediated Ca2+ transport.

Mammographic microcalcifications and breast cancer tumorigenesis: a radiologic-pathologic analysis

BACKGROUND

Microcalcifications (MCs) are tiny deposits of calcium in breast soft tissue. Approximately 30% of early invasive breast cancers have fine, granular MCs detectable on mammography; however, their significance in breast tumorigenesis is controversial. This study had two objectives: (1) to find associations between mammographic MCs and tumor pathology, and (2) to compare the diagnostic value of mammograms and breast biopsies in identifying malignant MCs.

METHODS

A retrospective chart review was performed for 937 women treated for breast cancer during 2000-2012 at St. Michael's Hospital. Demographic information (age and menopausal status), tumor pathology (size, histology, grade, nodal status and lymphovascular invasion), hormonal status (ER and PR), HER-2 over-expression and presence of MCs were collected. Chi-square tests were performed for categorical variables and t-tests were performed for continuous variables. All p-values less than 0.05 were considered statistically significant.

RESULTS

A total of 937 patient charts were included. About 38.3% of the patients presented with mammographic MCs on routine mammographic screening. Patients were more likely to have MCs if they were HER-2 positive (52.9%; p < 0.001). There was a significant association between MCs and peri-menopausal status with a mean age of 50 (64%; p = 0.012). Patients with invasive ductal carcinomas (40.9%; p = 0.001) were more likely to present with MCs than were patients with other tumor histologies. Patients with a heterogeneous breast density (p = 0.031) and multifocal breast disease (p = 0.044) were more likely to have MCs on mammograms. There was a positive correlation between MCs and tumor grade (p = 0.057), with grade III tumors presenting with the most MCs (41.3%). A total of 52.2% of MCs were missed on mammograms which were visible on pathology (p < 0.001).

CONCLUSION

This is the largest study suggesting the appearance of MCs on mammograms is strongly associated with HER-2 over-expression, invasive ductal carcinomas, peri-menopausal status, heterogeneous breast density and multifocal disease.