COL4A6 and adenocarcinoma: Further examination of collagen alpha-6 type IV (COL4A6) expression in tumor tissue for the two subtypes indicated that COL4A6 expression did not significantly correlate with the expression of the adenocarcinoma marker TT1 in adenocarcinoma (Additional file 1: Fig. S1C) but was significantly correlated with the SqCC marker TP63 (Additional file 1: Fig. S1D), suggesting it is upregulated during squamous differentiation associated with tumor development in a cell-type-specific manner [72].