Malignant Phyllodes Tumor of the Breast Metastasizing to the Vulva: ¹⁸F-FDG PET-CT Demonstrating Rare Metastasis from a Rare Tumor

Phyllodes tumors are extremely rare fibroepithelial neoplasms accounting for 0.3 to 0.5 % of all female breast tumors with an incidence of 2.1 per 1 million women [1]. They are classified histologically into benign, borderline and malignant varieties [2]. The majority of them are benign, with only 25 % being malignant. Surgery remains the mainstay of treatment. One characteristic is that although the malignant variety tends to metastasize and recur, the benign form has also been found to behave in a similar manner. Benign phyllodes tumor has a 21 % risk of local recurrence, while that of the malignant variety ranges from 20 to 32 %. In patients with malignant phyllodes tumor, the rate of distant metastases ranges from 25 to 40 % [3–6]. The most frequent sites of distant metastasis include the lungs, bone, heart and liver. Lymph nodal metastasis is uncommon as this tumor spreads by hematogeneous route [7]. Other sites for distant metastasis have been reported sporadically, including the duodenum, pancreas, brain, nasal cavity, forearm, parotid, skin, oral cavity, skeletal muscle, mandible and maxilla [8–10]. We present a rare case of recurrent malignant phyllodes tumor with metastasis to the vulva, which has not been reported in the literature to the best of our knowledge. A 49-year-old female who had undergone lumpectomy and locoregional radiotherapy 1 year previously for malignant phyllodes tumor of the right breast presented with difficulty in breathing and cervical lymphadenopathy. Chest X-ray showed multiple pulmonary nodules suggestive of metastasis. She was referred for restaging with 18F-fluorodeoxyglucose (FDG) positron emission tomography computed tomography (PET-CT) FDG PET-CT (Fig. 1). Maximum intensity projection (MIP) PET images revealed multiple FDG-avid enlarged cervical lymph nodes, bilateral pulmonary nodules along with left pleural effusion and extensive bone marrow metastases (a). The interesting finding was an intensely FDG-avid (SUV_max-21.4) subcutaneous soft tissue density lesion (measuring 2.0 × 2.2 × 2.0 cm) in the vulva, which was later proved to be metastatic from a malignant phyllodes tumor on FNAC (a–g; arrow). However, there was no evidence of local recurrence. This is in agreement with the existing literature on phyllodes tumor, showing that most recurrences with distant metastases occur without evidence of local recurrence, and the two do not seem to be related [11]. In spite of the scarce literature because of the rarity of the disease, there are sporadic reports highlighting the usefulness of FDG PET-CT in phyllodes tumor [12]. However, our case is unique in that over and above the extensive systemic metastases revealed, FDG PET-CT could detect metastatic deposit to the vulva, which is a very rare site for metastasis, even in the case of other common and rapidly metastasizing tumors. FDG PET-CT, thus is useful in recurrent phyllodes tumor and can demonstrate rare unsuspected sites of metastasis.

Fig. 1.

Maximum intensity projection (MIP) PET images revealed multiple FDG-avid enlarged cervical lymph nodes, bilateral pulmonary nodules along with left pleural effusion and extensive bone marrow metastases (a). The interesting finding was an intensely FDG-avid (SUV_max-21.4) subcutaneous soft tissue density lesion (measuring 2.0 × 2.2 × 2.0 cm) in the vulva, which was later proved to be metastatic from a malignant phyllodes tumor on FNAC (a–g; arrow)