OBJECTIVETo study the clinicopathologic and immunohistochemical features of atypical adenomatous hyperplasia (AAH) of lung.

METHODSEight cases of AAH of lung were studied by light microscopy and immunohistochemical staining for p16, thyroid transcription factor-1 (TTF-1), Ki-67, p53, epidermal growth factor receptor (EGFR) and c-erbB-2.

RESULTSThe mean age of the patients was 52 years. The male-to-female ratio was 1:3. Two patients were chronic smokers. The clinical symptoms were relatively non-specific. Three patients had past history of non-pulmonary tumors, while 4 patients had lung adenocarcinoma. CT scan revealed solitary or multifocal hyperdense opacities. Histologically, the lesions ranged from 1 mm to 6 mm in size. Two cases were solitary and 6 cases were multifocal. All were of high-grade lesions. Associated low-grade component was noted in 3 cases. There was no evidence of local recurrence or disease progression in the 7 patients with post-operative follow-up information available (mean duration of follow up = 23 months). Four patients had received chemotherapy as well. Immunohistochemical study showed variable positivity for p16 (5/8), TTF-1 (5/8), Ki-67 (with proliferation index ranging from 1% to 10%), p53 (1/8) and EGFR (1/8). The staining for c-erbB-2 was negative (0/8). Four cases of AAH were associated with pulmonary adenocarcinoma. The adenocarcinoma cells were diffusely positive for TTF-1 (4/4), variably positive for p16 (2/4), Ki-67 (with proliferation index ranging from 2% to 40%), p53 (1/4) and EGFR (3/4), and negative for c-erbB-2 (0/4).

CONCLUSIONSAAH of lung is associated with pulmonary adenocarcinoma. Diagnosis of AAH requires correlation with CT findings and pathologic examination.