Pharmacogenetics of Neoadjuvant MAP Chemotherapy in Localized Osteosarcoma: A Study Based on Data from the GEIS-33 Protocol

<b>Background:</b> Osteosarcoma is a rare disease, but it is the most frequent malignant bone tumor. Primary treatment consists of preoperative MAP (methotrexate (MTX), doxorubicin and cisplatin) chemotherapy followed by surgery and adjuvant chemotherapy. Pathological response to preoperative chemotherapy is one of the most important prognostic factors, but molecular biomarkers are lacking. Additionally, chemotherapy-induced toxicity might jeopardize treatment completion. We evaluated variants in genes involved in DNA repair and drug metabolism pathways as predictors of response to MAP-based treatment. <b>Material and Methods:</b> Germline polymorphisms in <i>MTHFR</i>, <i>SLC19A1</i>, <i>ABCB1</i>, <i>ABCC2</i>, <i>ABCC3</i>, <i>ERCC1</i>, <i>ERCC2</i> and <i>GSTP1</i> genes were determined for association studies in 69 patients diagnosed with localized osteosarcoma who enrolled in the prospective GEIS-33 trial. P-glycoprotein expression in tumor tissue was also analyzed. <b>Results:</b> In the multivariate analysis, the <i>ABCC2</i> rs2273697 (odds ratio [OR] 12.3, 95% CI 2.3-66.2; <i>p</i> = 0.003) and <i>ERCC2</i> rs1799793 (OR 9.6, 95% CI 2.1-43.2; <i>p</i> = 0.003) variants were associated with poor pathological response. P-glycoprotein expression did not correlate with pathological response. The <i>ABCB1</i> rs1128503 (OR 11.4, 95% CI 2.2-58.0; <i>p</i> = 0.003) and <i>ABCC3</i> rs4793665 (OR 12.0, 95% CI 2.1-70.2; <i>p</i> = 0.006) variants were associated with MTX grade 3-4 hepatotoxicity. <b>Conclusions:</b> Our findings add to the evidence that genetic variants in the ABC transporters and DNA-repair genes may serve as predictive biomarkers for MAP chemotherapy and contribute to treatment personalization.