Breast augmentation with implantation represents a challenge for subsequent radiographic imaging and pathological sampling. Fine-needle aspiration biopsy (FNAB) is an excellent technique to sample suspicious lesions that are adjacent to fragile implants. We report a case of a 51-year-old woman with breast implants presenting with an initial diagnosis of fibroadenoma by imaging studies. A definite diagnosis of mammary carcinoma with plasmacytoid cells was made on ultrasound (US)-guided FNAB of the breast mass with rapid on-site evaluation which initiated core needle biopsy of the mass and subsequent mastectomy with sentinel lymph node biopsy. Our case exemplifies the role of US-guided FNAB for the initial investigation of breast masses in patients with implants. In addition, the case illustrates the cytomorphological features of the tumor cells in primary neuroendocrine carcinoma of the breast.