Clinicopathologic analysis of 10 cases of pulmonary colloid adenocarcinoma and prognostic implication of invasive micropapillary component.

BACKGROUND: We aimed to investigate the clinicopathologic and histopathologic characteristics of colloid adenocarcinoma of the lung.

METHODS: We reviewed the data of 10 patients with colloid adenocarcinoma that met the definition and histopathologic criteria of the current classification of the World Health Organization. The clinicopathologic characteristics were analyzed. Comprehensive histologic review and immunohistochemical staining for TTF-1, ALK, CDX2, and MUC5AC as well as a molecular examination for EGFR and KRAS was performed.

RESULTS: Among 7 men and 3 women (mean age, 69.6 years), three patients had metastasis of the N2 lymph nodes; of these, two experienced recurrence, and one died of the disease. Remaining patients were all alive without metastasis or recurrence of disease. On gross examination, all tumors were circumscribed mucoid masses. Histologically, we observed the characteristic mucin pools that were distending and destroying the alveolar walls and low cellularity of tumor cells. Most tumor cells were tall columnar cells with basally-located bland-looking nuclei and intracytoplasmic mucin. CDX2 and TTF-1 were partially positive in all and four patients, respectively. MUC5AC was positive in all cases, at least focally. Seven cases showed peribronchiolar metaplasia-like, ciliated tumor cells. Three patients with N2 lymph node metastasis showed mild (N = 2) and moderate (N = 1) cytologic atypia in primary tumors. Presence of stromal invasion and/or micropapillary pattern was common findings of cases with N2 lymph metastasis.

CONCLUSION: Colloid adenocarcinoma is a rare variant of lung adenocarcinoma with distinct clinicopathologic characteristics. The frequently seen ciliated tumor cells may suggest that this tumor might originate from a metaplastic process. Majority had indolent clinical course but presence of stromal invasion or micropapillary pattern may reflect aggressive behavior of colloid adenocarcinoma and may indicate poor prognosis.