In 2014, a 60-year-old non-smoker female with past medical history of recurrent bronchitis came to visit for 3 months of dry cough and exertional dyspnea, which remained unchanged after treatment with clarithromycin. At chest examination, bilateral diffuse crackles could be appreciated, without wheezing. No touchable lymphadenopathies were present. Echocardiogram was normal, while on chest X-ray (CXR; Figure 1) parenchymal infiltrates were documented, which were more evident in the left lung. A total body CT scan (TB CT; Figure 2) revealed diffuse parenchymal infiltrates with mediastinal and hilar lymphadenopathies, suggestive of sarcoidosis but also compatible with a malignant origin. A vascularized pathologic (3 cm) lymph node was also detected in the right axillary region and surgically removed 8 days after the CXR and 2 days after the CT scan, together with other nodes of the same station, for diagnostic purposes. At histologic examination, localization/metastasis of poorly differentiated epithelial neoplasia was found in only one of the resected nodes (Figures 3A-C), whereas in the others giant cell granulomatous epithelioid sarcoid-like reaction was detected (Figure 3D). An exhaustive and multidisciplinary diagnostic workup was thus initiated to determine the putative primary origin of cancer cells. Their immunophenotype (cytokeratin 7+, AE1/AE3+, TTF1+, and p63-) was coherent with axillary lymph node localization of lung adenocarcinoma. In detail, the cytokeratin panel expression confirmed the epithelial origin, while the positivity of thyroid transcription factor 1 (TTF-1) was a highly specific marker for lung as primary origin and suggested the adenocarcinomatous lineage of differentiation. The absence of p63 expression allowed to exclude squamous differentiation as well as neuroendocrine carcinomas. Subsequent molecular analysis documented the absence of actionable genetic targets since mutational analysis revealed EGFR wt, KRAS wt, ALK not translocated, and HER2/neu not amplified. We then proceeded with a first bronchoscopy to study deeper the lung parenchyma and find the primary site of malignant growth. A transbronchial biopsy (TBB) was then performed, revealing bilateral superior bronchial stenosis in the absence of histologic neoplastic infiltration (Figures 3E,F). To complete the disease stage and/or eventually to detect a distant site of origin of the neoplastic cells, a whole-body positron emission tomography was performed and evidenced supra- and subdiaphragmatic pathologic lymphadenopathies in the absence of putative primary mass detection (Figure 4). Since no tumor masses were demonstrated by imaging, a second bronchoscopy with TBB was thus repeated to deeply analyze the lung parenchyma. Quite unsuspectedly, the TBB obtained specimens that were free from neoplastic cells but rich of sarcoid non-necrotizing epithelioid granulomas. Steroid treatment (prednisone, 1 mg/kg) was started, with rapid improvement on symptomatology. After 1 month, a TB CT showed reduction in parenchymal infiltrates and lymphadenopathies without extra-thoracic neoplastic or sarcoid localizations. Being in the presence of carcinoma featuring lung epithelial lineage of origin vs metastatic lung cancer without detectable primary mass, in the absence of the expression of actionable targets, platinum-based conventional chemotherapy (cisplatin-pemetrexed) was started, and steroids were tapered until 10 mg/day. The TB CT at the end of three cycles of adjuvant chemotherapy confirmed the presence of some fibrotic branches, compatible with stage IV pulmonary sarcoidosis, without oncologic localizations (Figure 5). A timeline with all relevant data from this clinical case is available in Figure 6. The steroid regimen was gradually reduced to a maintenance of 5 mg/day over a period of 1 year. At 5 years from diagnosis, the result at follow-up is still negative, with no neoplasm recurrence and with good control of sarcoidosis in the absence of steroid treatment.