Class of 2007 Abstract / Objectives: The objective of this study was to determine the cost-effectiveness of using the Invader® UGT1A1 Molecular Assay to identify patients at risk of experiencing neutropenia from irinotecan monotherapy and FOLFIRI. Methods: Publicly available search engines were used to search for literature reporting the rate, treatment, and cost of adverse events and the population rate of genotypes. Drug acquisition costs were determined using average wholesale prices. Additional costs were determined using the Physicians’ Fee and Coding Guide. Monte Carlo Simulations were performed to reveal average cost, average effectiveness, and 95% confidence intervals. Tornado diagrams were derived to identify variables most likely to affect the outcomes and sensitivity analyses. Results: Monte Carlo simulations of monotherapy revealed a mean cost of treatment with genotype assay information of $6,620 (SD: $3,235; 95% CI: $5,408 to $15, 258) and an effectiveness ratio of 0.877 (SD: 0.328; 95% CI: 0 to 1). Without the genotype assay information the mean cost of treatment was $7,358 (SD: $4,183; 95% CI: $5,083 to $14,883) and the effectiveness ratio was 0.764 (SD: 0.425; 95% CI: 0 to 1). Monte Carlo simulations of FOLFIRI data showed a mean cost of treatment with genotype assay information of $6,105 (SD: $3,438; 95% CI: $4,706 to $14,556) and an effectiveness ratio of 0.858 (SD: 0.349; 95% CI: 0 to 1). When genotype information was unknown, the mean cost of FOLFIRI was $6,833 (SD: $4,288; 95% CI: $4,331 to $14,181) and the effectiveness ratio was 0.746 (SD: 0.435; 95% CI: 0 to 1). Conclusions: Genotyping patients exposed to irinotecan monotherapy or FOLFIRI may be a cost-effective means of identifying at risk patients but the results from this study while favorable are not statistically significant.