Biologic Downstaging Observed With a Pulmonary Collision Tumor

Abstract

Collision tumors are a rare entity in which 2 distinct neoplastic cellular populations invade each other and coalesce to form a single focal lesion. This case report describes a pulmonary collision tumor emerging from the rapid progression of 2 large-cell carcinoma lesions of the lung, including 1 nodule with clear cell features and another with basaloid features. The collision of these 2 histologically rare nodules resulted in the biologic downstaging of disease. This report provides unique insights into the biology of pulmonary collision tumors and its implications for diagnostic staging and therapeutic management. Collision tumors are a rare entity in which 2 distinct neoplastic cellular populations invade each other and coalesce to form a single focal lesion. This case report describes a pulmonary collision tumor emerging from the rapid progression of 2 large-cell carcinoma lesions of the lung, including 1 nodule with clear cell features and another with basaloid features. The collision of these 2 histologically rare nodules resulted in the biologic downstaging of disease. This report provides unique insights into the biology of pulmonary collision tumors and its implications for diagnostic staging and therapeutic management. Collision tumors are a rare phenomenon whereby 2 distinct neoplastic cellular populations invade each other and coalesce to form a single focal lesion. Previous reports have described pulmonary collision tumors arising from heterogeneous tumor types.1Wang Z. Si J. Liu J. Primary pulmonary cancer colliding with metastatic choriocarcinoma.J Thorac Dis. 2015; 7: E28-E32PubMed Google Scholar,2Nakata S. Nagata Y. Sugaya M. et al.Primary pulmonary collision cancer consisting of large cell carcinoma and adenocarcinoma.Ann Thorac Surg. 2005; 80: 340-342Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar In this report, a pulmonary collision tumor emerging from independent, synchronous large-cell carcinoma lesions that resulted in the biologic downstaging of disease is described. The patient is an 88-year-old man with a peripheral right middle lung field opacity on chest radiography found during preoperative evaluation for transurethral resection of benign prostatic hypertrophy. Follow-up chest computed tomography (CT) demonstrated 2 distinct pulmonary nodules (15 mm and 13 mm) in the periphery of the right middle lobe (Figures 1A-1C ). The patient is a former 50-pack-year smoker with no personal or family history of lung cancer. Owing to the onset of the coronavirus disease 2019 pandemic, follow-up CT scan was delayed 5 months after initial presentation and showed interval growth and coalescence of the pulmonary nodules into a single 3.2-cm mass (Figures 1D, 1E). Positron emission tomography/CT imaging showed a 4.2 × 2.4-cm hypermetabolic nodule in the right middle lobe (standard uptake value of 12.3) without evidence of metastatic disease (Figure 1F). The patient underwent a robot-assisted right middle lobe wedge resection. Intraoperative frozen section of the mass demonstrated carcinoma with small round blue cells, necrosis, and mitotic features. Consequently, a completion lobectomy was performed robotically and uneventfully. His postoperative recovery was unremarkable. Final pathologic examination demonstrated a vaguely barbell-shaped biphasic large-cell carcinoma (4.5 × 3.1 × 2.8 cm) that appeared to be grossly and microscopically contiguous (Figure 2A). On histologic evaluation, 1 tumor nodule had clear cell features and the other had basaloid features (Figures 2B-2E). Both components were negative for lineage-specific immunohistochemistry stains (thyroid transcription factor 1, NapsinA, p40, p63, CK5/6, synaptophysin, chromogranin, CD56, insulinoma-associated protein 1; Figures 2D, 2F). Pathologic staging was consistent with a stage IB (pT2b N0) tumor. The patient was referred to a medical oncologist to discuss adjuvant chemotherapy options but elected to pursue a conservative strategy of