Screen-detected mucinous breast carcinoma: potential for delayed diagnosis

To describe the imaging features of 34 screen-detected mucinous carcinomas lesions.

The BreastScreen Western Australia (WA) database between January 1991 and December 2003 was searched. During this period, 214,507 women were screened and 2745 cases of invasive carcinoma and 45 cases of mucinous carcinoma were recorded. Case notes, radiology films and pathology reports of patients with mucinous carcinoma were reviewed. Thirty-four radiologically detected pure mucinous carcinomas are described.

Of the pure mucinous carcinomas, the average age at diagnosis was 65 years (range 48-82 years), which was higher than that of other women with breast cancer (average age 60 years) screened at BreastScreen WA. Characteristic mammographic features of mucinous carcinoma are well-circumscribed masses with lobulated margins (26/34). Only 39% (11/28) of tumours were detected at ultrasound, as the smaller lesions less than 15mm in diameter were often isoechoic with normal fat. Where histological grade was reported at excision, most (25/26) were low to medium-grade tumours (Bloom, Richardson and Elston grade I and II). A significant number of lesions (13/34) were evident on the previous screening examination where they were misinterpreted as benign lesions. However, none of these cases had positive axillary lymph nodes at final diagnosis.

Although mammographically benign appearances of mucinous carcinoma caused a delay in diagnosis in 38% of the present cases, mucinous breast carcinomas have a favourable prognosis, as they are often low-grade tumours and rarely metastasize. Delay in diagnosis for these tumours in a screening programme may not lead to a significant adverse outcome for most women.