A case of complicated cyst mimicking breast cancer

Abstract

Complicated cysts are frequently seen in US findings. We experienced a woman in her 40s with a left breast mass with an atypical B-mode image with score 4 on elastography (according to the Tsukuba elasticity score). Core needle biopsy (CNB) and US-guided vacuum-assisted biopsy (US-VAB) were performed, and the mass turned out to be a complicated cyst, not cancer. A malignancy was suspected on B-mode. A surrounding slight color Doppler signal was detected. The elasticity score was 4, and the fat-lesion-ratio (FLR) was 17.2. The mass was evaluated as category 5 (The Japan Association of Breast and Thyroid Sonology categorization¹⁾). The pathology of the lesion was consistent with complicated cyst. Follow-up US about 1 year later detected no abnormality. Elastography is useful for differentiation of benign from malignant breast masses. In that case, an elasticity false-positive finding may support malignancy. It is important to be aware of the possibility of false-positive cases determined to be on the malignant side on elastography when diagnosing complicated cysts.