Gene profiling of metastatic small intestinal squamous cell carcinoma after lung squamous cell carcinoma surgery: a case report

BACKGROUND: Isolated metachronous metastatic small intestinal squamous cell carcinoma is rare, and it is sometimes is difficult to determine whether small intestinal squamous cell carcinoma is metastatic by immunohistochemistry alone. At present, there is no literature analyzing the gene profile of metastatic small intestinal squamous cell carcinoma. CASE DESCRIPTION: We met a 62-year-old male patient who had a history of lung squamous cell carcinoma surgery. He was admitted for simultaneous jejunal squamous all carcinoma, gastric adenocarcinoma, rectal adenocarcinoma. Endoscopic resection was performed for gastric cancer and rectal cancer, surgical resection was performed for jejunal squamous cell carcinoma, and docetaxel adjuvant chemotherapy were performed after surgery. No tumor recurrence was found in the reexamination in august 2021, and the patient was still alive during telephone follow-up before submission. This case presented two key challenges: (I) we could not determine whether the small intestinal squamous cell carcinoma was primary or metastatic; and (II) whether the patient, who had four different cancers, carried a genetic mutation that causes disease. We performed next generation sequencing (NGS) on four kinds of tissues and white blood cells, and found that the EGFR gene exhibited the same pathogenic mutation in both the lung and small intestine (c.2155G>Tp.G719C and c.2303G>Tp.S768I), and that the PPM1D gene had the same unidentified mutation (c.1787A>G:p.H596R) in two organs, therefore jejunal squamous cell carcinoma is considered as metastasis of lung squamous cell carcinoma. We found the FGFR4 mutation (c.1162g>A:p.g388r) in the blood and four kinds of tissues, which may be pathogenic and significantly increase the risk of cancer in patients. CONCLUSIONS: Genetic testing helped us identify the source of metastases, helped us find two rare mutations in the squamous cell carcinoma EGFR gene, and helped us find that FGFR4 (c.1162G>A:p.G388R) mutation may play an important role in tumor development.