Differential expression of basement membrane type-IV collagen α1, α2, α5 and α6 chains among the histological subtypes of adenoid cystic carcinoma

Six distinct alpha(IV) chains in the basement membrane (BM) of adenoid cystic carcinoma (ACC) of the salivary gland were immunohistochemically examined by anti-alpha(IV) chain-specific antibodies, and their expressions were compared with the histological subtypes and the expressions of cytokeratin 19 (CK19), cytokeratin 14 (CK14) and alpha-smooth muscle actin (alpha-SMA) and Ki-67. In the BM of normal salivary ducts, alpha1(IV), alpha2(IV), alpha5(IV) and alpha6(IV) chains were continuously stained, but alpha3(IV) and alpha4(IV) chains were negative. In the tubular and cribriform subtypes of ACC, tubules with continuous staining of alpha5(IV) and alpha6(IV) chains showed the biphasic-staining pattern among the expressions of CK19, CK14 and alpha-SMA. However, in cancer-cell nests with discontinuous or negative staining of alpha5(IV) and alpha6(IV) chains, the biphasic pattern was ambiguous. In the solid subtype, the staining of alpha1(IV) and alpha2(IV) chains was discontinuous, the staining of alpha5(IV) and alpha6(IV) chains was negative and the biphasic-staining pattern was unclear. The mitotic activity of cancer cells analyzed by the Ki-67 labeling index was significantly related to the expression of alpha5(IV) and alpha6(IV) chains in the cribriform subtype. These results suggest that BM irregularity with the differential expression of alpha(IV) chains in ACC closely relates to cell proliferation, cell differentiation and histological structure.