Thymidylate synthase polymorphisms and immunohistochemistry in non-small cell lung cancer

Abstract

11101 Background: Recently, pemetrexed has been introduced into the treatment of non-small cell lung cancer (NSCLC). There's evidence that pemetrexed appears to be more efficient in non squamous NSCLC including adenocarcinoma (AC) and large cell carcinoma (LCC). TS represents a major target enzyme of pemetrexed. We evaluated the expression of TS among different histological types of NSCLC and its association with functional genetic polymorphisms of the TS gene. Methods: Archived tumor samples from 312 individuals with NSCLC were analyzed. Immunohistochemistry (IHC) was performed using a mouse monoclonal antibody to TS. TS stained sections were scored for cytoplasmic and nuclear localization. For each compartment, the tumor was evaluated for the estimated percentage of positive cells with the greatest intensity within the tumor. Intensity was scored on a scale of 0–4. A score of 3–4 was classified as high expression. Genotyping of TS-VNTR including the G/C SNP and TS1394del6 was performed by PCR based RFLP techniques. Genotypes supposed to be associated with low expression were grouped (group A: 2R/2R or 2R/3RC or 3RC/3RC + -6/-6) and compared to genotype groups associated with high expression (group B: 2R/3RG or 3RC/3RG or 3RG/3RG + -6/+6 or +6/+6). Results: IHC and polymorphisms could be performed successfully in 312 (100%) and 287 (92%), respectively. Distribution of histology was as follows: 50% AC, 42% squamous cell carcinoma (SCC), 3% LCC and 5% mixed or other histological subtypes. Group B genotypes were significantly more present in SCC than in AC (49% vs 23%, p=.002). Tumors with group B genotypes were more likely to display high nuclear staining intensity than group A tumors (30% vs. 17%, p=.077). A similar but not significant trend was seen for cytoplasmic staining intensity. There was no significant difference between histological subtypes of NSCLC with respect to TS protein expression. AC were more common than SCC to show a G1 differentiated tumors (8% vs 1%, p<.001). No difference between genotype groups were observed with respect to grading. Conclusions: TS polymorphisms are significantly associated with histology subtypes in NSCLC. These results represent a potential explanation for efficacy differences of pemetrexed in NSCLC and warrants further investigations. [Table: see text]