Metastatic mediastinal malignant tumors of gastrointestinal origin with occult primary lesions: a case report

TL;DR

A rare case of metastatic gastrointestinal cancer in the chest area with no identifiable primary tumor is reported, highlighting diagnostic challenges and the need for advanced testing.

Contribution

This case report highlights the diagnostic challenges of GI-origin mediastinal CUP and emphasizes the need for molecular profiling and advanced diagnostics.

Findings

A mediastinal mass with GI immunohistochemical features was found in a patient with no identifiable primary tumor.

Conventional imaging failed to detect the primary lesion despite comprehensive evaluations.

Molecular profiling and ctDNA analysis are suggested for accurate diagnosis and treatment planning.

Abstract

Cancer of unknown primary origin (CUP), accounting for 3–5% of malignancies, poses significant diagnostic challenges because of the absence of identifiable primary lesions. While common occult primary tumors involve the lung or pancreas, gastrointestinal (GI)-originated mediastinal metastases are exceedingly rare. A 54-year-old male presented with chest tightness and dyspnea. Imaging revealed a 45.5 × 36.3 mm anterior mediastinal mass. Pathological evaluation postresection revealed metastatic moderately differentiated adenocarcinoma with immunohistochemical (IHC) features (CK20+/Villin+/CK7−/TTF-1−) suggestive of GI origin. Despite comprehensive evaluations (gastroscopy, PET-CT), no primary lesions were detected. Chronic atrophic gastritis (C2) was noted, but malignancy was excluded. This case underscores the diagnostic complexity of GI-profile mediastinal CUP and highlights limitations in conventional imaging. Molecular profiling (e.g., KRAS/NRAS/BRAF mutation) and advanced diagnostics (ctDNA analysis) are critical for accurate classification and tailored therapy. Long-term surveillance remains essential, as 12% of CUPs reveal primaries during follow-up.

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