RESUMEN
BACKGROUND: Mucinous colloid lung adenocarcinoma is an uncommon variant of lung carcinomas with similar features to tumours seen in the gastrointestinal tract. To distinguish between these tumours and other mucinous lung tumours, such as mucinous bronchioloalveolar cell carcinomas and metastatic mucinous lesions could be difficult with small biopsy specimens from fine needle aspiration. CLINICAL CASE: The case is described of a 49-year-old female with history of dyspnoea and cough with bloody sputum and weight lose. Thorax axial computed tomography demonstrated a right lower lobe spiculated mass with calcifications. Transthoracic computed tomography- guided fine needle biopsy reported negative results, and the biopsy obtained with video-assisted thoracic surgery was useful for an adequate cytology report of a colloid variant of mucinous lung adenocarcinoma. CONCLUSION: Video-assisted thoracic surgery is an appropriate option for obtaining a larger specimen in those cases where small biopsies are inconclusive for the diagnosis of thoracic pathologies such as malignant tumours.