Rectal metastasis as the initial presentation of primary lung adenocarcinoma with an EGFR L858R mutation: a case...

Non-small cell lung cancer (NSCLC) accounts for approximately 80% of all Lung cancers, and 40% of patients with lung cancer present with distant metastases at diagnosis. Symptomatic rectal metastasis from primary lung adenocarcinoma before the onset of lung symptoms is exceedingly rare. This is the first report to describe an uncommon case of rectal metastasis from an EGFR L858R-mutant primary lung adenocarcinoma.

A 79-year-old male presented to the hospital for worsening constipation. Colonoscopy revealed a rectal mass, but initial biopsies revealed only chronic rectal mucosal inflammation. The patient received symptomatic treatment to stimulate defecation, but his symptoms of constipation worsened. As symptoms progressed to dyspnoea, cough, expectoration, bilateral lower limb weakness, and poor appetite, imaging revealed a mixed ground-glass nodule with poorly defined margins in the apical segment of the right upper lobe. Imaging also revealed thickening of the rectal wall in the mid-to-lower segments with multiple small perirectal lymph nodes. Immunohistochemical analysis of both the rectal puncture biopsy specimen and the white nodules resected during the laparoscopic peritoneal biopsy consistently revealed CK7 (+), TTF-1 (+), Napsin A (+), CK20 (-), and CDX2 (-) staining, which confirmed rectal metastasis from primary lung adenocarcinoma. After the laparoscopic transverse colostomy was performed, the patient began treatment with aumolertinib mesilate tablets that target the EGFR L858R mutation and received palliative radiotherapy for the rectal metastatic lesion.

Although rectal metastasis harbouring EGFR L858R mutations from primary lung adenocarcinoma is extremely rare, clinicians should have a low threshold for pulmonary low-dose spiral CT. In addition, histopathologic analysis by immunohistochemistry combined with molecular diagnostics is critical for a timely and accurate diagnosis and to distinguish rectal metastases from primary rectal malignancies.