Unexpected tumor localization in a patient admitted for fibrotic ILD: The value of systematic bronchoscopic biopsy

Pulmonary lymphangitic carcinomatosis (PLC) is an aggressive form of pulmonary metastasis. Its fibrotic presentation can mimic interstitial lung disease (ILD), making diagnosis challenging when the primary tumor is unknown. We report the case of a 69-year-old patient admitted for the etiological assessment of chronic ILD at the fibrotic stage. While the initial clinical and radiological presentation suggested a classical interstitial pathology, systematic bronchial biopsies performed during bronchoscopy revealed poorly differentiated carcinomatous proliferation, with immunohistochemistry suggesting a pancreatico-biliary origin. This case highlights the crucial importance of systematic biopsy during bronchoscopy for any ILD, even when appearing fibrotic, to avoid overlooking an occult neoplastic pathology.