15-Lipoxygenase-2 expression in benign and neoplastic lung: An immunohistochemical study and correlation with tumor grade and proliferation

15-Lipoxygenase-2 (15-LOX-2) is an arachidonic acid-metabolizing enzyme expressed in prostate, lung, skin, esophagus, and cornea. In the benign prostate, it is expressed in differentiated secretory epithelial cells, where its enzymatic product 15-HETE may regulate transcription by activating the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ). 15-LOX-2 and 15-HETE formation are reduced in prostate carcinoma. The distribution of 15-LOX-2 in the normal lung and its expression in lung carcinomas has not been reported and was investigated in the current study by using immunohistochemistry and tissue microarrays (TMAs). In benign lung, 15-LOX-2 immunostaining was noted exclusively in type II pneumocytes, which are known to express PPARγ. Of 160 lung carcinomas, 15-LOX-2 was expressed in non-small cell carcinomas (NSCLC), including 33 of 69 (48%) adenocarcinomas, with 10 of 16 (63%) bronchioloalveolar carcinomas immunopositive. Fourteen of 55 (25%) squamous cell carcinomas and 2 of 14 (14%) large cell carcinomas showed weak immunostaining. All 19 neuroendocrine tumors were negative. Better differentiated NSCLCs showed greater 15-LOX-2 expression, with a significant inverse correlation between 15-LOX-2 immunostaining and tumor grade (P < 0.03). A significant inverse correlation was also noted between 15-LOX-2 immunostaining and tumor cell proliferation (Ki-67 immunostaining; P < 0.0001). These findings suggest a possible role of 15-LOX-2 in regulating secretory differentiation and proliferation in benign lung and NSCLCs, particularly adenocarcinomas.