In this report, we present a case of tumor-to-tumor metastasis characterized by malignant SFT harboring metastatic prostatic cancer. This case is consistent with the previously proposed diagnostic criteria for tumor-to-tumor metastasis [11], namely, (Ⅰ) the existence of more than one primary tumor; (Ⅱ) the recipient tumor representing a true benign or malignant neoplasm; (Ⅲ) the donor neoplasm representing a true metastasis with established growth in the host tumor, not the result of contiguous growth or embolization of tumor cells; and excluding (Ⅳ) tumors that have metastasized to the lymphatic system, where lymphoreticular malignant tumors are already present.
Generally, SFT is a rare mesenchymal neoplasm, which frequently arises in intrathoracic sites including the pleura and lung. Macroscopically, SFT appears as a smooth, firm, and lobulated mass. Microscopically, the neoplasm displays an erratic organization of round, ovoid to spindle-shaped cells with a patternless architecture. They possess “staghorn” vessels and a hyalinized stroma, especially in perivascular regions. Immunohistochemically, the immunostaining of tumor cells is typically positive for vimentin, CD34, STAT6 and Bcl-2 and negative for keratin [12].
While SFT has been acknowledged as a suitable niche for harboring metastases because of its rich vascularity to filter microemboli from other tumors, SFT is an extraordinarily rare recipient for tumor-to-tumor metastasis. To date, only nine SFT recipients of tumor-to-tumor metastasis have been described in the literature (Table 1), including five intrathoracic lesions, one intraabdominal, one spinal intradural, and two in the soft tissues (thigh and back) [2–10]. The most common metastatic donor to SFT in previous reports was breast cancer.
Table 1
Cases of tumor-to-tumor metastasis to a solitary fibrous tumor recipient
Publication | Donor | Recipient | Relationship |
Petraki et al., 2003(2) | Bladder carcinoma | SFT-pleura | Synchronous |
Chen et al., 2004(3) | Lung carcinoma | SFT-thigh | Synchronous |
Gonullu et al., 2010(4) | Breast carcinoma | SFT-pleura | Synchronous |
Sen et al., 2010(5) | Breast carcinoma | SFT-mesentery | Metachronous |
Kragel et al., 2011(6) | Renal cell carcinoma | SFT-pleura | Synchronous |
Scheipl et al., 2014(7) | Male breast carcinoma | SFT-back | Synchronous |
Frank et al.,2016(8) | Breast carcinoma | SFT-pleura | Metachronous |
Tosic et al.,2018(9) | Lung carcinoma | SFT- intradural | Synchronous |
Shishido et al.,2019(10) | Pulmonary typical carcinoid | SFT-lung | Synchronous |
Our case report | Prostatic carcinoma | Malignant SFT-lung | Synchronous |
The lung SFT in this report was diagnosed as a malignant neoplasm with histological characteristics of pleomorphism, hypercellularity, nuclear atypia, more than 4 mitoses per 10 high-power fields, and tumor necrosis. To our knowledge, this report is the first to describe a case of lung malignant SFT as recipient of tumor-to-tumor metastasis.
Prostatic cancer is also an uncommon donor in tumor-to-tumor metastasis. We were able to identify 15 previously reported cases of donor prostatic cancer in tumor-to-tumor metastasis, none of which involved SFT. The most common recipient tumor was meningioma (7 cases) [13], followed by renal cell carcinoma (6 cases) [14–16], follicular adenomas of the thyroid gland (1 case) [17], renal oncocytoma (1 case) [18].This case is also the first reported in the literature to involve prostatic cancer metastasizing to SFT.
Tumor-to-tumor metastasis can have synchronous or metachronous onset (Table 1). We present the case with synchronous onset of prostatic cancer metastasizing to lung SFT. This evidence then guided us to confirm the origin and donor site of metastatic prostatic cancer.