Complicated breast cysts on sonography: is aspiration necessary to exclude malignancy?

To determine the incidence of breast cancer in women presenting for fine needle aspiration of sonographically diagnosed complicated breast cysts.

Institutional review board approval was obtained. A retrospective study was performed of 186 consecutive women who presented for fine needle aspiration of 243 sonographic complicated cysts detected by clinical examination or imaging between January 2002 and August 2003. Sonographic complicated cysts were defined as those meeting most but not all criteria for simple cysts similar to current Breast Imaging Reporting and Data System classification. We excluded solid masses, cysts with solid components, intracystic masses, and simple cysts. Prospective mammography, ultrasound, and procedure reports were reviewed. A case was considered positive if cytology, core needle biopsy, or surgical excision was positive for cancer. Final diagnosis was established by biopsy, cytology, clinical resolution, or stability over time.

One of 243 (0.4%) lesions proved malignant (95% confidence interval 0-1.94%); 210/243 (86.4%) of cases yielded fluid on aspiration. Of 141 samples submitted to cytology, 138 (97.9%) were benign and 3 (2.1%) atypical. All cases of atypia were benign at surgical excision. Ninety five of 243 (39.1%) aspiration samples with typical cyst fluid were discarded. A total of 33/243 (13.6%) cases did not yield fluid, 1 of which was positive for cancer. Thirty cases underwent core needle or excisional biopsy for imaging discordance with benign results.

Breast cancer presenting as a complicated cyst by ultrasound was rare (0.4%, 95% confidence interval 0-1.94%). These results provide support for classification of complicated cysts as probably benign.