Study: Cancers in extremely dense breasts are often mammographically occult

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Cancers in extremely dense breasts occur in younger women, are more often mammographically occult, and appear to be phenotypically different from those arising in other density groups, according to a study published in the October issue of Annals of Surgical Oncology.

The study was a retrospective review of a prospectively maintained database performed by Nimmi Arora, MD, from the department of surgery at Memorial Sloan-Kettering Cancer Center, Evelyn H. Lauder Breast Center in New York City, and colleagues.

Eligible patients had Stage 1 to 3 cancers, were treated between January 2005 and June 2007, and had estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2 measurements and films were available for review.

Arora and colleagues classified density at presentation as 1 to 4 using the Breast Imaging Reporting and Data System (BI-RADS) classification and 1,323 patients were included in the study. Significant differences across the four density groups were present in age, race, multicentricity/focality and presence of an extensive intraductal component (EIC).

When density was combined into two groups, after adjustment for age, only an EIC and mammographically occult cancers were significantly more common in the dense groups. Extremely dense breasts (BIRADS density 4) more commonly had luminal A tumors, lobular cancers, multicentricity, and 41 percent had mammographically occult tumors.

Greater density was associated with increased mastectomy use, with 61 percent of the extremely dense group having mastectomy versus 43 percent of those of lesser density.

“Our finding that multifocality, multicentricity and infiltrating lobular carcinomas were more frequent in extremely dense breasts may help to explain the increased use of mastectomy in this group,” wrote Arora and colleagues.

In summary, this study confirms that the association between increased mammographic breast density, young patient age and occult tumors persists despite improvements in mammographic technique, the researchers said.

“We identified an association between extremely dense breasts and the luminal A molecular subtype of breast cancer, as well as between extremely dense breasts and cancers of lobular histology. Consistent with these associations, we did not find any correlation between density and tumor prognostic factors, calling into question the preferential use of mastectomy in women with dense breasts,” concluded Arora and colleagues.