Imaging findings in mucin-containing carcinomas of the breast: correlation with pathologic features.

OBJECTIVE: Breast carcinomas may contain varying quantities of extracellular mucin. The purpose of this study was to correlate the mammographic and sonographic appearance of mucin-containing carcinomas of the breast with the histologic features of these tumors.
MATERIALS AND METHODS: The tumor registry and breast imaging files at our institution identified 34 women with 37 mucin-containing breast carcinomas for which mammographic and histologic slides were available for review. By consensus, two radiologists determined the mammographic margin characteristics (circumscribed, microlobulated, indistinct, spiculated) and, when available, the sonographic properties of the carcinomas. Doubling time in days was estimated from sequential mammograms when possible. A pathologist reviewed the histologic slides and divided the 37 carcinomas into three categories based on the percentage by volume of mucin seen: pure mucinous (> or = 90% mucin), 23 cases; moderately mucinous (< 90% and > 30% mucin), seven cases; and minimally mucinous (< or = 30% mucin), seven cases. To determine the contribution of varying percentages of mucin to the radiologic appearance of the tumors, the margin characteristics were correlated with the histologic percentage of mucin, microscopic margin appearance (displacing or infiltrating), nuclear grade (I, II, III), and lymph node status.
RESULTS: Tumors with circumscribed and microlobulated margins on mammography had a higher percentage of mucin histologically (p < .01; chi 2). A trend of slower growth rate on mammograms, lower histologic nuclear grade, and less frequent axillary node involvement were also seen in tumors with a higher percentage of mucin. Spiculated mammographic margins were seen when there were decreasing volumes of mucin and when tumor margins histologically were infiltrating; these tumors had higher nuclear grades and more frequent axillary node involvement (p < .01).
CONCLUSION: The radiologic and pathologic correlation of mucin-containing breast carcinomas demonstrates that lesions with higher percentages of mucin have mammographic appearances that reflect less aggressive histologic margins, lower nuclear grades, and slower growth rates. Carcinomas that have small percentages of mucin have mammographic and histologic characteristics of more aggressive, invasive ductal carcinomas.