[Expression of ALK protein in 7 371 pulmonary adenocarcinoma samples, with analysis of clinicopathologic features]

To study the expression of ALK protein in pulmonary adenocarcinoma as detected by Ventana immunohistochemistry, with correlation of clinicopathologic features.

Immunohistochemical study for ALK protein using Ventana ALK (D5F3) kit was carried in 7 371 pulmonary adenocarcinoma samples. The clinicopathologic features were subsequently analyzed.

ALK fusion protein was detected in 446 of the 7 371 lung adenocarcinoma samples studied (6.05%). The ALK positivity rate in small biopsy samples was higher than that in surgical specimens [9.02% (153/1 696) versus 5.16% (293/5 675); P<0.01]. ALK fusion protein expression correlated with patient age, sample type and smoking history. ALK positivity rate in each age group increased with younger patient age. ALK positivity rate was 45.45% (10/22) in patients younger than 30 years old. The positivity rate of ALK fusion protein in adenocarcinoma in-situ, minimally invasive adenocarcinoma and invasive adenocarcinoma was 0, 0.48% (2/418) and 5.63% (291/5 165), respectively. The differences of ALK positivity rate amongst different subtypes had statistical significance (P<0.01). Invasive mucinous adenocarcinoma had highest ALK positivity rate, followed by invasive adenocarcinoma with predominantly solid pattern.

ALK fusion protein is more often found in young patients with pulmonary adenocarcinoma, especially in those younger than 30 years old. ALK fusion protein is rarely expressed in early-stage pulmonary adenocarcinoma. Invasive mucinous adenocarcinoma and invasive adenocarcinoma with solid pattern have higher ALK positivity rate than other adenocarcinoma subtypes.