Early uptake and continuous accumulation of thallium-201 chloride in a benign mixed tumor of soft tissue: case report

Abstract

A case of benign mixed tumor of the soft tissue in a 64-year-old Japanese male is presented. He noticed a painless, elastic hard mass sized 3 cm in the right knee, which gradually grew larger and harder in the last 5 years. Magnetic resonance imaging demonstrated a mass lesion embedded in the subcutaneous tissue with low and high signal intensity at T1- and T2-weighted images, respectively. Tl-201 scintigraphy showed an early uptake of Tl-201 within the lesion at 10 minutes after injection, which was slightly decreased but still continued at 2 hours later. The patient underwent a resection of tumor, and the pathological diagnosis was a benign mixed tumor of soft tissue without high vascularity, characterized by histological features similar to pleomorphic adenomas in the salivary glands. Immunohistochemical study proved expression of Na+/K+-ATPase of tumor cells. Overexpression of Na+/K+-ATPase of the tumor might be responsible for the early uptake of Tl-201, and poor vascular structure in this tumor might lead to continuous accumulation. The Tl-201 scintigraphic features of mixed tumor of soft tissue are assessed to resemble those of malignant soft tissue tumors.

Figure 1

MRI showing a mass lesion embedded in the subcutaneous tissue on the medial posterior side of the right knee, demonstrating low and high signal intensity in T1- and T2-weighted images (arrows in upper and lower), respectively.

Figure 2

Tl-201 scintigraphy of the whole body at the early phase (left). Tl-201 was uptaken into the tumor in the right knee at the early scan (right upper) and continuously accumulated at the delayed scan (right lower).

Figure 3

Comprehensive immunohistochemical staining: a, representative section by H-E stain (×200); b, Cytokeratin (CK) AE1/AE3 (×200); c, CK CAM5.2 (×200); d, CK 34βE12 (×200); e, EMA (×200); f, desmin (×200); g, α-smooth muscle actin (×200); h, p63 (×200); i, S-100 protein (×200); j, CD31 (×200); k, CD34 (×200); l, p53 (×200); m, bcl-2 (×200); n, p16 (×200); o, Ki-67 (×200).

Figure 4

Histological feature of mixed tumor of soft tissue with a variety of components; epithelial component E, myoepithelial component M, and osseous metaplasia O (H-E stain, ×40). Tumor cells overexpressing anti-Na⁺/K⁺-ATPase antibody (small window in right lower corner, immunohistochemical staining, ×400).