Pulmonary tumour thrombotic microangiopathy (PTTM) is a rare pulmonary complication observed in 0.9–3.3% of autopsies of patients with metastatic carcinomas that are characterised by multiple tumour microemboli associated with proliferation of intimal fibromuscular cells and the formation of fibrin thrombi in the small pulmonary arteries and arterioles.^{1, 2} Clinically, patients with PTTM often present with progressive dyspnoea and severe pulmonary hypertension, and develop acute right side heart failure.³

We report here an autopsy case of PTTM caused by a gastric carcinoma. In the present study, the expression PDGF and PDGF receptor (PDGFR) were detected in tumour cells. Moreover, the overexpression of PDGF was detected in alveolar macrophages. A possible contribution of alveolar macrophages in PTTM is discussed.

A 64-year-old male patient was referred to Nagasaki University Hospital for treatment of a gastric tumour. Physical examination including auscultation was normal. Gastrointestinal endoscopy showed thickening and tortuosity of folds of the stomach wall, so-called leather bottle-like appearance. An abdominal CT scan showed a thickening of the stomach wall and swelling of multiple lymph nodes. Remarkable symptoms of respiration were not detected. A chest CT scan was negative.

At autopsy, the stomach wall was found to be diffusely thickened, and ulceration was identified in the prepyloric area. Abdominal lymph nodes were markedly involved. The left and right lungs weighed 310 g and 340 g, respectively. No macroscopic thrombi were found in the pulmonary arteries or main branches, and neither gross emboli nor visible nodules of cancer metastasis were noted on the cut surfaces of the lungs.

Light microscopy showed a poorly differentiated carcinoma infiltrating the wall of the stomach. Lymphatic vessel infiltration was remarkable with multiple involvement of abdominal lymph nodes. In the lungs, most of the small arteries and arterioles were stenotic or occluded by fibrocellular intimal proliferation and thromboemboli with or without tumour cells. In some pulmonary vessels, organised thromboemboli with recanalisation were observed. All of these pathological features of the pulmonary vessels were consistent and characteristic of PTTM.

Immunohistochemically, proliferating fibromuscular cells in the intima were positive for α-smooth muscle actin (Dako, Glostrup, Denmark) (figure 1D). Immunoreactivity of pancytokeratin (AE1/AE3, Dako) was indicated in the carcinoma cells (figure 1E) in a pulmonary artery. Moderate expressions of PDGF (figure 2A,C) and PDGFR (figure 2D,E) (Santa Cruz Biotechnology, Santa Cruz, CA, USA) were localised to the fibromuscular intimal cells, smooth muscle and endothelial cells in constricted small arteries. The immunoreactivity of PDGF and PDGFR was also detected in tumour cells (figure 2A,C–E). In addition, overexpression of PGDF-A was detected in alveolar macrophages around small pulmonary arteries with constricted or plexiform remodelling (figure 2A,B). Phosphorylated Src (Acris Antibodies, Hiddenhausen, Germany) expression was also identified in the tumour cells in the vessels (figure 2F).