Mucoepidermoid carcinoma arising in Warthin's tumor of the parotid gland: Clinicopathological characteristics and immunophenotypes

Abstract

Mucoepidermoid carcinoma (MEC), an extremely rare tumor, arises from the epithelial component of preexisting parotid Warthin tumors (WT). Among the 309 cases of surgically resected WTs in Chinese PLA General Hospital and Beijing Shijitan Hospital of Capital Medical University, 5 cases (1.6%) fulfilled the criteria for MECs transformed from WTs. Clinicopathological characteristics of MECs was demonstrated in order to avoid misdiagnosis of this rare type of tumor. All the 5 patients, 3 males and 2 females, presented painless masses in the parotid gland. MECs were located inside or at the edge of WTs, with an obvious transitional zone between WT and MEC. Basal cells of WTs and epidermoid cells of MECs were strongly positive for cytokeratin CK5/6, CK34βE12, and P63; whereas negative for CK7, CK20, and CEA. Mucous cells of MECs were positive for CK7, CEA, as well as periodic acid-Schiff (PAS), whereas negative for CK5/6, CK34βE12, CK20, and P63. MECs patients were followed up for 25-69 months after surgery, presenting no evidence of recurrence or metastasis. Collectively, MECs arising from WT is very rare. The pathological diagnosis was based on histological morphology, especially the transitional zone between WT and MEC.

Figure 1. Major imaging findings for patients.

(A) CT scanning in case 1 displayed circular nodule shadow in the right parotid gland. (B) Enhanced scanning identified cystic or necrotic tumor. (C) MRI displayed irregular shaped lesions in the right parotid gland globe in Case #5. (D) MRI enhanced scan revealed MECs tumors (yellow arrow highlighted parotid gland, red arrow highlighted the tumor).

Figure 2. Gross appearance of the tumor derived from Case #5.

Solid sections were highlighted in grayish-yellow or grayish-brown color. Tumor had invaded the outside border of the capsule.

Figure 3

Histological characteristics of tumors in Case #1 (A) and #2 (B). Low-grade malignancies consisted of a large number of mucous cells and a small number of epidermoid cells. Tumors derived from Case #3 (C) and #4 (D): Low-grade malignancies were composed of a large number of epidermoid cells and a small number of mucous cells. Tumor derived from Case #5 (E) was high-grade malignancy contained a large number of epidermoid cells with anaplasia and a small number of mucous cells.

Figure 4. CK7 was positive in mucous and epidermoid cells in MECs.

Figure 5

CEA was positive in mucous cells of MEC in Case #1 (A) and #2 (B) whereas negative in epidermoid cells of MEC. CEA was negative in mucous and epidermoid cells of MECs in Case #3 (C), #4 (D) and #5 (E).

Figure 6. CK5/6 was highly overexpressed in epidermoid cells of MEC, whereas negative in mucous cells.

Figure 7. P63 was positive in epidermoid cells in MECs.

Figure 8. CK34βE12 was positive in epidermoid cells in MECs.

Figure 9

Ki67 index of MEC was 1% in Case #1 (A) #2 (B) and #3 (C); 2% in Case #4 (D); and 5% in Case #5 (E).

Figure 10. PAS was positive in mucous cells in MECs.