Case report: 125I seed implantation for rare malignant solitary fibrous tumor in the pelvic cavity: a case report

Abstract

Solitary fibrous tumor (SFT) is a rare spindle cell tumor, benign or low-grade malignant, with an extremely low possibility of occurrence of malignant solitary fibrous tumor (MSFT). Surgery is an effective way for treating SFT, but it is often difficult to resect completely due to a large size, with a high recurrence rate and mortality rate after operation. Additionally, SFT is relatively resistant to chemotherapy, and there is a lack of effective systemic drug treatment. These lead to certain difficulties in the treatment of SFT. We report a case of a rare MSFT in the pelvic cavity. With a history of recurrence after two surgeries, this patient underwent surgical removal combined with ¹²⁵I seed implantation at our hospital in the context that the tumor could not be completely removed because it was large and adhered to surrounding tissues; after up to 43 months of progression-free survival (PFS), the patient underwent ¹²⁵I seed implantation alone, and achieved a complete remission, with a PFS up to 35 months. ¹²⁵I seed implantation can be a safe and effective treatment option for unresectable MSFT as well as a potential solution to repeated local recurrence.

Keywords: 125I seeds; MSFT; brachytherapy; malignant solitary fibrous tumor; recurrence.

Figure 1

(A) and (B) were abdominal wall tumor(7×5×8 cm), left pelvic tumor(5.5×3.5×7 cm) and right iliac paravascular tumor(8.5×3×5 cm) before treatment, while (C) and (D) were left pelvic and right iliac paravascular tumors without recurrence 43 months after surgery+¹²⁵I seed implantation.

Figure 2

(A):hypercellular areas(HE ×100). (B):hypercellular area with atypical nuclei and some evident mitotic figures(HE ×200). (C):Tumor cells are diffusely positive for CD99(IHC×200). (D):Tumor cells are diffusely positive for STAT6 (IHC ×100).

Figure 3

(A) and (B) were behind bladder tumors before treatment with size of about 4×3×5.0 cm, 3.0×2.0×2.5cm respectively, and (C) and (D) were two years after ¹²⁵I seed implantation.

Figure 4

(A) was the recurrence of abdominal wall tumor with a size of about 4.0×2.5×4.5 cm before treatment in 2016/1, (B) was 6 months after ^125I seed implantation, (C) was the recurrence of abdominal wall tumor(3.6×1.5×3.0 cm) and behind bladder tumors(5.0×3.0×5.0 cm) before treatment in 2018/10, (D) was 4 months after ¹²⁵I seed implantation.