Imaging findings and accuracy of core needle biopsy in mucinous carcinoma of the breast

Background: Diagnosis of mucinous carcinoma can be difficult due to its benign appearance on mammograms and ultrasonographic (US) images. In the light of the rather scarce literature, core needle biopsy (CNB) has proved useful in diagnosing mucinous lesions. Purpose: To assess mammographic, US, and CNB findings of mucinous breast tumors and to correlate them with final histology obtained in therapeutic surgery. Material and Methods: From 2000-2006, 25 mucinous carcinomas detected with CNB were surgically removed. The mammography, US, and CNB results were analyzed and correlated with final histology. Results: Ninety-six percent of the mucinous carcinomas (24/25) were visible with US. All except two of the 24 tumors were solid masses. All the mixed-type lesions (group 2) were hypoechoic and had irregular or lobulated margins and heterogeous internal echotexture. The US features were more variable among the 14 pure mucinous carcinomas (group 1) and the six US visible mucinous carcinomas with cancerous cells outside the tumor (group 3). Fifty-seven percent of group 1 and 50% of group 3 tumors had clearly lobulated or irregular margins. Fifty-seven percent of group 1 and 67% of group 3 cancers were hypoechoic. A vast majority of these tumors had heterogenous echotexture. Seventy-one percent (17/24) of the lesions visible with US had posterior acoustic enhancement. Eighty percent (20/25) of the mucinous carcinomas were classified as BI-RADS 4 lesions in US. All the lesions with images available were visible on mammograms, where most of the tumors were seen as a high-density circumscribed lesion and classified as BI-RADS 4 lesions, while none were classified as BI-RADS 1, 2 or 5. The sensitivity and positive predictive value of CNB regarding mucinous carcinoma was 100%. Conclusion: CNB was found to be a highly reliable diagnostic tool for diagnosing mucinous carcinoma in this selected material. US findings of pure mucinous carcinoma were variable, however, all reached BI-RADS 4 category. The presence of posterior acoustic enhancement beneath a solid breast lesion should raise suspicion of mucinous carcinoma. Most of the tumors appeared as BI-RADS 4 lesions in US and in mammography thus making both a useful tool for raising a suspicion of malignancy in mucinous cancers.