組織蛋白酶K膜染色：鑑別診斷唾液腺透明細胞癌與黏液性表皮樣癌的新興免疫組織化學標記物

Abstract

唾液腺透明細胞癌（hyalinizing clear cell carcinoma, HCCC）是一種罕見的唾液腺惡性腫瘤，其腫瘤由透明細胞和嗜酸性腫瘤細胞所構成，有時也會出現黏液樣細胞。這些腫瘤細胞通常存在於玻璃樣變性的間質中，排列成不規則的巢狀、索狀或小樑狀結構。然而，透明細胞不僅存在於HCCC腫瘤中，其他唾液腺腫瘤中也可能出現，這使得HCCC與其他具有透明細胞的腫瘤區分變得困難。特別是黏液性表皮樣癌(mucoepidermoid carcinoma, MEC)也可能同時具有透明細胞、嗜酸性癌細胞以及黏液細胞，因此明確診斷通常需要利用螢光原位雜交技術(FISH)進行基因檢測。大多數的HCCC具有EWSR1::ATF1 融合基因，而MEC則高達80%病例有MAML2 基因轉位。不過，FISH的價格高昂且並非所有病理實驗室都能夠執行，因此尋找其他有用的標誌物對於HCCC和MEC的鑑別診斷至關重要。 除了HCCC外，EWSR1::ATF1 融合基因也存在於其他腫瘤中，如透明細胞肉瘤。已有研究表明ATF1可以增加透明細胞肉瘤中組織蛋白酶K的表達，使其成為在透明細胞肉瘤的診斷上有用的標誌物。基於HCCC和透明細胞肉瘤具有相同的ATF1融合基因，我們針對組織蛋白酶K是否可以作為診斷HCCC的標誌物進行了研究。我們回顧性地蒐集了22例經FISH證實有EWSR1基因轉位的HCCC病例，以及21例MEC病例，進行組織蛋白酶K的免疫組織化學染色 (IHC)，以觀察這兩種唾液腺腫瘤之間免疫組織蛋白酶K的表達是否存在差異。結果顯示，所有的HCCC都會表現免疫組織蛋白酶K的細胞質染色，而MEC則只有19%病例的細胞質染色呈現陽性。此外，HCCC還具有局部性或瀰漫性的免疫組織蛋白酶K的特殊膜染色現象，而MEC則完全不會表現膜染色。為了評估組織蛋白酶K在唾液腺腫瘤的表現，我們進一步進行了另外10種唾液腺腫瘤的組織蛋白酶K之IHC表達，結果顯示，具有上皮細胞或肌上皮細胞組成的唾液腺腫瘤，比較容易會有細胞質及細胞膜的組織蛋白酶K染色陽性。不過詳細機制還尚不明確，需要進一步研究來探討HCCC的組織蛋白酶K膜染色，以及組織蛋白酶K對於唾液腺腫瘤的影響。 總結來說，我們的研究表明，組織蛋白酶K可以作為HCCC和MEC鑑別診斷的新標誌物，尤其是透過在HCCC中觀察到的特殊膜染色。此外，我們也分析了組織蛋白酶K在諸多唾液腺腫瘤中的表達，為使用組織蛋白酶K協助診斷唾液腺腫瘤提供參考。

Hyalinizing clear cell carcinoma (HCCC) is a rare malignant tumor of the salivary gland. HCCC comprises variable amounts of clear cells and eosinophilic cells with occasional mucocytes. Tumor cells usually arrange in irregular nests, cords, or trabecular architecture, separating by hyalinized stroma. Clear cells are not uncommon in other salivary gland tumors, and sometimes it is difficult to differentiate HCCC from other salivary gland tumors with a clear cell component, especially clear-cell variant mucoepidermoid carcinoma (MEC) which also has clear cells, eosinophilic cells and mucocytes. Genetic tests like fluorescence in situ hybridization (FISH) are usually required for definite diagnosis. The majority of HCCCs harbors EWSR1::ATF1 fusions, while up to 80% of MECs have MAML2 rearrangements. However, FISH is expensive and not available in most pathological laboratories. Therefore, finding a useful marker for differential diagnosis between HCCC and MEC is essential. The genetic EWSR1::ATF1 fusion in HCCC is also observed in other tumors such as clear cell sarcoma. It has been found that the ATF1 can increase cathepsin K expression in clear cell sarcoma, which makes it a useful marker in the diagnosis. In this study, we aimed to test if cathepsin K could serve as a useful marker based on the fact that both HCCC and clear cell sarcoma harbor the same ATF1 fusions. Retrospectively, 22 HCCC cases with EWSR1 rearrangement confirmed by FISH and 21 MEC cases were collected. Cathepsin K immunohistochemical staining (IHC) was performed to determine if there was any differential expression of cathepsin K between these two types of salivary gland tumors. The result showed that all HCCC cases had cytoplasmic staining for cathepsin K while only 19% of MEC cases showed positive cytoplasmic staining. Moreover, HCCC also exhibited a unique membranous staining in variable proportion of tumor cells ranging from focal to diffuse areas, whereas none of the MEC cases displayed cathepsin K membranous staining. Moreover, to evaluate cathepsin K expression in salivary gland tumors, we further conducted cathepsin K IHC staining on ten different types of salivary gland tumors. We observed that salivary gland tumors with epithelial cell or myoepithelial cell components tend to exhibit cytoplasmic and membranous cathepsin K staining. The detailed mechanism remains unclear, and further research is required to determine the membranous staining of cathepsin K in HCCC and the effects of cathepsin K on salivary gland tumors. In summary, our study showed that cathepsin K IHC is a novel marker in the differential diagnosis between HCCC and MEC, especially the unique membranous staining found in HCCC. The expression of cathepsin K in salivary gland neoplasms was also analyzed, providing evidence supporting using cathepsin K in the diagnosis of salivary gland tumors.