To test the hypothesis that CD44 standard (CD44[s]) and its other variants, CD44v6 and CD44v7-8, might be useful markers of squamous differentiation in epithelial tumors.
We studied expression of CD44(s), CD44v6, and CD44v7-8 using immunohistochemistry in human tumors that had squamous differentiation, glandular differentiation, or both arising in the colon, stomach, esophagus, lung, pancreas, gallbladder, or uterus/cervix, as well as in adjacent nonneoplastic tissues. Formalin-fixed, paraffin-embedded archival tissue specimens of 33 adenosquamous tumors were used. All were stained with monoclonal antibodies against a conserved portion of CD44(s) and its variants, CD44v6 and CD44v7-8, using the avidin-biotin peroxidase method.
CD44(s) and its variants consistently and strongly stained areas of tumors with well-developed squamous differentiation. These markers also consistently and strongly stained normal squamous mucosa. Reactivity for CD44 and its variants was lacking in normal glandular type epithelium and in adenocarcinomas composed entirely of well-differentiated mucin-producing glands. Areas of well-differentiated carcinoma, both squamous and adenocarcinoma, were consistent with respect to both extent and intensity of staining. Staining in lymph nodes was similar to that in the primary tumors, with well-differentiated squamous foci being consistently positive, well-differentiated mucin-producing adenocarcinoma foci consistently negative, and poorly differentiated foci showing variable staining. Although staining was less intense with the variants, it followed the same staining pattern as found for CD44(s). No differences in the extent or intensity of staining were identified in the metastatic versus primary tumor foci, nor was any difference identified between superficial and deeply invasive areas of primary tumors.
Our study shows that CD44(s) and its variants are good markers of squamous epithelial differentiation in several types of normal epithelium and tumors, and that these markers can identify areas of well- to moderately differentiated elements in adenosquamous neoplasms. However, poorly differentiated tumors show an inconsistent staining pattern with CD44, such that it cannot be used as a reliable and practical marker of squamous differentiation in poorly differentiated neoplasms.