Mucinous (colloid) breast cancer: mammographic and US features with histologic correlation

Mucinous carcinoma of the breast presents with different survival rates in pure and mixed types. The purpose of this study was to correlate the mammographic and ultrasonographic findings of mucinous carcinoma with histologic features in different types and mucin rates.

Thirty-four patients (2.3%) had mucinous cancer after retrospective review of the 1439 breast cancers diagnosed between 1990 and 1996. Twenty-seven patients, 19 pure and eight mixed type of mucinous carcinomas of the breast, were included in this study to evaluate the imaging findings. In 22 of these, the microscopic slides were available and re-evaluated to estimate the volume of extracellular mucin. The volume of the extracellular mucin was classified histologically as: (+), less than 50% of mucin; (++), 50-80% of mucin; and ( ), more than 80% of mucin. Mammographic features with emphasis on margin characteristics and sonographic echo pattern of tumors were correlated with histologic findings.

Ten cases (53%) of pure mucinous type carcinomas had a circumscribed mass lesion on the mammograms. The well-defined, lobulated margins of the masses were well correlated with pure histologic type (P<0.01; chi(2) analysis) Two-thirds of these tumors had high volume extracellular mucin. All mixed type mucinous carcinomas demonstrated poorly defined or spiculated margins with no relation to the mucin rates (P<0.01). The sonographic appearances of the tumors showed correlation with histologic types. Most of the pure type carcinomas (53%) were seen with isoechogenic echo texture relative to that of subcutaneous fat, while all of the mixed type carcinomas were hypoechogenic (P<0.01).

The mammographic and sonographic features of mucinous breast carcinoma show differences in pure and mixed types of the tumor. The most common mammographic appearance of pure mucinous carcinomas with high percentages of mucin is a mass lesion having well-defined margins, which is isoechogenic relative to fat on the sonographic examination. Pure type of carcinomas with small percentages of mucin and mixed type carcinomas have more aggressive imaging characteristics.