Value of CK14 and CD56 immunostaining in distinguishing small cell carcinoma from squamous cell carcinoma of the esophagus.

Primary small cell carcinoma of esophagus (SCC) is a rare disease but has more aggressive behavior than esophageal squamous cell carcinoma (SQC). The distinction of SCC from SQC is very important therapeutically. Few systematic studies of immunohistochemical analysis to differentiate primary esophageal SCC with concomitant SQC, and adjacent normal esophageal epithelium have been reported. The objective of this study is to know the immunohistochemical markers in distinguishing SCC from SQC of esophagus. We studied 6 cases of primary esophageal SCC histologically and immunohistochemically using 15 different antibodies including a cytokeratin (CK) panel and neuroendocrine markers. Pure SCCs were identified in 2 of the 6 cases (33.3%), and the remaining 4 cases (66.7%) were found to exhibit combined SCC with an SQC component. Among the combined types, in situ SQC was observed in all 4 cases (100.0%) and invasive SQC was observed in 3 cases (75.0%). Among the normal esophageal epithelia specimens (n=7), CK14 expression was seen 6 out of 7 (85.7%) specimens and CKAE1/3 in 5 out of 7 (71.4%) specimens. CD56 was more frequently expressed among the SCC specimens (4/6; 66.7%) than among the SQC specimens (0/4; 0%; p = 0.07). The expression of p53 protein in SCC (4/6; 66.7%) and SQC (3/4; 75.0%) specimens was significantly more frequent than in normal esophageal epithelium (0/7; 0%; p = 0.02 each). Neurone-specific enolase (NSE), synaptophysin, and CKAE1/3 were expressed in 83.3%, 66.7%, and 66.7% of the SCC cases (n=6), respectively. NSE expression was significantly more frequent in SCC specimens (5/6; 83.3%) (p = 0.02) than in normal esophageal epithelium (0/7; 0%; p = 0.02). However, the frequencies of NSE expression in SCC (5/6; 83.3%) and SQC (2/4; 50%) were not significantly different. All of the SQC specimens (n=4) expressed CK14 and CKAE1/3. The CK14 expression was significantly more frequent in SQC specimens (4/4; 100.0%) than in (p = 0.04) SCC specimens (1/6; 16.6%; p = 0.04). These findings suggest that the CK14 and CD56 may be useful markers for differentiating SQC from SCC and vice versa. The p53 may also be useful to differentiate normal esophageal epithelium from SCC or SQC tissue.