Lobular breast carcinoma metastasis to skeletal muscle, two case reports diagnosed by ultrasound guided FNA with evaluation of the roles of interventional cytopathology

Skeletal muscle metastasis from breast carcinoma is a relatively rare clinical entity. We report two cases of breast cancer metastatic to the skeletal muscle, diagnosed by ultrasound guided fine needle aspiration (US‐FNA) biopsy done by interventional cytopathologists at an outpatient cytopathology center. Our two patients presented with lower anterior neck firmness and chest wall mass, respectively. Ultrasound evaluation of our first case demonstrated hypo‐echoic thickened anterior strap muscles while in the second case there was significant distortion of the anatomy from previous surgeries. It was necessary to proceed with FNA biopsy even when their ultrasound findings were equivocal, to establish a definite rapid diagnosis. The immediate onsite evaluation findings were suggestive of malignancy in both cases with subsequent core biopsy confirming the diagnosis of metastatic breast carcinoma. In cytopathology, point‐of‐care (POC) ultrasound is used as an adjunct tool that offers visual guidance during FNA of nonpalpable masses and enables sampling of lesional "hot" spots to ensure specimen adequacy. Studies have demonstrated a reduction in FNA nondiagnostic rates with the use of ultrasound‐guidance consequently reducing health care costs associated with nondiagnostic FNAs. US‐FNA also provides adequate samples for cell block preparations. Metastatic lobular carcinoma of the breast has a wide range of clinical presentations and a high level of suspicion is advised. Cytopathologists‐performed US‐FNA is a proven, less‐invasive, cost‐effective tool that provides timely cytologic diagnosis.

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