Lung Adenocarcinoma With Subintimal Spread Along the Pulmonary Artery: A Case Report.

Pulmonary vascular invasion is a well-recognized feature of advanced lung cancer and is associated with poor prognosis. Vascular invasion usually refers to either microscopic invasion into small vessels or direct invasion of great vessels; however, longitudinal subintimal spread within the pulmonary artery has not been reported. We describe the case of a 77-year-old woman with a pulmonary nodule followed for two years, which enlarged to 23 mm with cavitation. A right upper lobectomy with mediastinal lymph node dissection was performed. Histopathology showed that the tumor was predominantly adenocarcinoma. In addition, longitudinal invasion was identified beneath the intima of the pulmonary artery, located between the lumen and elastic fibers without extension into the lumen or outside the vessel wall. Notably, in this subintimal invasive area, the central portion consisted of adenocarcinoma, whereas squamous differentiation was confined to the surrounding margins. The primary nodule measured 2.5 cm, but the total extent of subintimal invasion was 6 cm. The pathological stage was pT3N0, stage IIB. This case demonstrates a previously unreported pattern of pulmonary artery invasion by lung adenocarcinoma with characteristic marginal squamous differentiation, expanding the spectrum of vascular invasion in lung cancer.