A case of rare primary cystic-type squamous cell carcinoma of the breast that could be preoperatively diagnosed.

Primary squamous cell carcinoma of the breast (SCCB) is a rare disease, with a worldwide incidence <0.1%. In many cases, it is clinically characterized by rapid growth. Cyst formation due to central necrosis of the tumor accompanies its growth of the tumor in approximately 60-80% of all cases. Furthermore, it is considered difficult to diagnose SCCB solely on the basis of findings from diagnostic imaging. For large intracystic tumors, mammotome biopsy or core needle biopsy (CNB) is rarely performed. Instead, fine-needle aspiration (FNA) targeted at the tumor inside the cyst is often performed. The accurate diagnosis rate of SCCB using FNA is lower than that for ordinary-type breast cancer. If the cyst is large, the solid tumor shadow outside the cyst behind or around the cyst may be masked or hidden by the large cyst, which can sometimes yield an unclear view of the tumor shadow or make it impossible to visualize the shadow. In the present case, the contents within the cyst were completely aspirated and collected during the first step (FNA), thereby yielding a clearer, complete view of the solid tumor located outside the cyst. Thus, the subsequent step (CNB) was able to be performed in a more accurate and reliable manner. The combined use of FNA and CNB proved to be useful in making a preoperative diagnosis of SSCB accompanying a cyst.