An update on clinicopathological, immunohistochemical, and molecular profiles of colloid carcinoma of the lung

Colloid carcinoma is a rare subtype of lung adenocarcinoma characterized by abundant pools of extracellular mucin and scant malignant epithelium. Because of the rarity of these tumors, many of the reported clinicopathological and immunohistochemical characteristics are contradictory. Moreover, the molecular alterations that underlie these tumors are unknown. We present the clinicopathological, immunohistochemical, and molecular features of 13 cases of colloid carcinoma of the lung. The patients were 9 women and 4 men between the ages of 48 and 86 years. Surgical resection and staging were performed in all patients. Seven patients were in stage T₁N₀M₀, 3 in T₂N₀M₀, 2 in T₂N₁M₀, and 1 in T₂N₀M₁. The tumor was 100% mucinous in 9 patients, whereas in 4 cases, the lesions consisted of 50% to 90% mucin pools with the remainder being a noncolloid adenocarcinoma component ranging in morphology from bronchioalveolar to acinar, papillary, solid, or mixed patterns. Follow-up ranged from 35 to 128 months. Three patients died, 1 of disease and 2 of unrelated causes. The remaining 10 patients are alive at the time of reporting, 3 with recurrent disease. Immunohistochemical studies showed CK7, CK20, and CDX2 expression in all tumors, whereas TTF-1, surfactant A, and napsin A were not present or were only focally positive in most cases. Analysis showed KRAS mutations in 2 cases. All tumors were negative for ALK gene rearrangement and EGFR mutation. Our study highlights the clinicopathological, immunohistochemical, and molecular features of lung colloid adenocarcinoma and attempts to clarify some misconceptions regarding this rare tumor.