Background: We report the case of a small cell carcinoma of the upper third of the esophagus associated to a squamous carcinoma in situ (collision tumor). The meaning of collision tumors remains
uncertain. Recently, molecular biology techniques have been used to establish the origin of multiple neoplastic lesions in different organs.
Case Report: The case of a women with a small cell carcinoma of the esophagus associated to a squamous
carcinoma in situ of the overlying epithelium is described. The patient is currently suffering from
multiple bilateral hepatic metastases and pleural lesions. Sections from pre-operative esophageal
biopsies were tested with several antibodies (Chromogranine, Cytokeratin 20, NSE, ACTH, VIP,
Calcitonin, p53) and DNA was extracted for p53 loss of heterozygosity and microsatellite instability
assay. Microscopy observation showed a lesion confined to the submucous layer, associated with
areas of mild-severe dysplasia in the overlying squamous epithelium. Immunohistochemistry showed negativity in both in small cell and squamous cell carcinoma for all markers except chromogranine and p53. Microsatellite stability and LOH in D17S250, D17S513, and D17S830 were observed in both tumors.
Conclusions: In this rare case of collision tumor, the results of immunohistochemistry and molecular analysis were the same in the two tumor components, suggesting that they probably share common
evolutionary pathways based on loss of p53.

Keywords: collision tumor, esophageal carcinoma, p53, Loss of Heterozygosity