Variations of P40 and P63 Immunostains in Different Grades of Esophageal Squamous Cell Carcinoma: A Potential Diagnostic Pitfall.

The distinction of esophageal squamous cell carcinoma (SCC) from adenocarcinoma (adenoCA) using targeted therapies has become critical for small biopsies. In the United States, esophageal SCC is relatively uncommon compared with AdenoCA, with only few detailed immunohistochemical (IHC) studies on esophageal SCC. We characterized p40 and p63 IHC across various grades of squamous differentiation in esophageal SCC and compared their sensitivities between esophageal SCC and adenoCA. Twenty-eight esophageal SCC and 26 esophageal adenoCA (control group) samples were stained for p40, p63, and CK5/6. All hematoxylin-and-eosin-stained SCC slides were reviewed. Tumors were graded according to the World Health Organization classification: well, moderately, or poorly differentiated (WD, MD, and PD, respectively). Considering morphological heterogeneity, individual differentiation components within the same tumor were scored separately (0% to 100%) according to the proportion of immunoreactive cells and marked as positive (≥5%) or negative (<5%). Among 28 esophageal SCC, 15 had mixed intratumoral differentiation. There were 16 WD, 19 MD, and 14 PD components. P40 immunoreactivity was significantly lower in WD than in MD or PD components (P<0.001), P63 immunoreactivity patterns were similar (P<0.001), while CK5/6 showed no differences (P>0.05). The sensitivities for SCC components were 98% (P40), 100% (P63), and 100% (CK5/6), while those for esophageal AdenoCA were significantly lower: 4% (P40), 4% (P63), and 8% (CK5/6). P40 and P63 were sensitive and specific for routine esophageal SCC diagnosis. However, their immunostaining was significantly lower in WD SCC than in higher grade tumors. IHC results for small biopsy specimens should be interpreted carefully, particularly in WD components.