5-Fluorouracil (5-FU) and oral fluoropyrimidines, such as capecitabine, are widely used in the treatment of cancer, especially gastrointestinal tumors and breast cancer, but their administration can produce serious and even lethal toxicity. This toxicity is often related to the partial or complete deficiency of the dihydropyrimidine dehydrogenase (DPD) enzyme, which causes a reduction in clearance and a longer half-life of 5-FU. It is advisable to determine if a DPD deficiency exists before administering these drugs by genotyping DPYD gene polymorphisms. The objective of this consensus of experts, in which representatives from the Spanish Pharmacogenetics and Pharmacogenomics Society and the Spanish Society of Medical Oncology participated, is to establish clear recommendations for the implementation of genotype and/or phenotype testing for DPD deficiency in patients who are candidates to receive fluoropyrimidines. The genotyping of DPYD previous to treatment classifies individuals as normal, intermediate, or poor metabolizers. Normal metabolizers do not require changes in the initial dose, intermediate metabolizers should start treatment with fluoropyrimidines at doses reduced to 50%, and poor metabolizers are contraindicated for fluoropyrimidines.

Objective Although KRAS mutation status has been identified as a strong predictor of response to anti-epidermal growth factor receptor (EGFR) therapies, not all wild-type patients respond. The lethal-7 (let-7) family of microRNAs regulates KRAS activity. A functional polymorphism (rs61764370) has been described in the let-7 complementary site (LCS6). We hypothesized a possible association between this KRAS let-7 LCS6 polymorphism and the response to anti-EGFR treatments in KRAS and BRAF wild-type metastatic colorectal cancer patients (mCRC). Materials and methods We studied the association of the KRAS let-7 LCS6 polymorphism with the response in 100 refractory mCRC patients treated with anti-EGFR antibodies. To assess the real effect of this polymorphism in relation to the treatment administered, we also studied this association in an independent cohort of patients treated exclusively with chemotherapy. The KRAS let-7 LCS6 polymorphism was genotyped using the BioMark system in blood and tumor DNA samples. The BRAF V600E mutation was analyzed in tumor samples. Results The KRAS let-7 LCS6 G-allele showed a statistically significant association with nonresponse to anti-EGFR-based treatment: 31.9% of patients with the T/T genotype presented a complete or a partial response versus no patients with T/G or G/G genotypes (P=0.004). No statistically significant differences were observed in the patients who received chemotherapy only. Conclusion These data support the pharmacogenetic role of the KRAS let-7 LCS6 polymorphism in predicting the efficacy of anti-EGFR-based therapy in mCRC patients with the KRAS and the BRAF wild-type genotype.

Purpose: Chemotherapy plus anti-EGFR is standard first-line therapy in RAS wild-type (wt) metastatic colorectal cancer (mCRC), but biomarkers of early response are clinically needed. We aimed to define the utility of ctDNA to assess early response in patients with mCRC receiving first-line anti-EGFR therapy. Experimental Design: Prospective multicentric study of tissue patients with RAS wt mCRC treated with first-line chemotherapy plus cetuximab undergoing sequential liquid biopsies. Baseline and early (C3) ctDNA were analyzed by NGS. Trunk mutations were assessed as surrogate marker of total tumor burden. RAS/BRAF/MEK/EGFR-ECD were considered mutations of resistance. ctDNA results were correlated with clinical outcome. Results: One hundred patients were included. ctDNA was detected in 72% of patients at baseline and 34% at C3. Decrease in ctDNA trunk mutations correlated with progression-free survival (PFS; HR, 0.23; P = 0.001). RAS/BRAF were the only resistant mutations detected at C3. An increase in the relative fraction of RAS/BRAF at C3 was followed by an expansion of the RAS clone until PD, and was associated with shorter PFS (HR, 10.5; P < 0.001). The best predictor of response was the combined analysis of trunk and resistant mutations at C3. Accordingly, patients with “early molecular response” (decrease in trunk and decrease in resistant mutations) had better response (77.5% vs. 25%, P = 0.008) and longer PFS (HR, 0.18; P < 0.001) compared with patients with “early molecular progression” (increase in trunk and/or increase in resistant mutations). Conclusions: ctDNA detects early molecular response and predicts benefit to chemotherapy plus cetuximab. A comprehensive NGS-based approach is recommended to integrate information on total disease burden and resistant mutations. See related commentary by Eluri et al., p. 302

Patients harbouring the UGT1A1*28/*28 genotype are at risk of severe toxicity with the standard irinotecan dose. However, this dose is considerably lower than the dose that can be tolerated by UGT1A1*1/*1 and *1/*28 patients. This randomised phase II trial evaluated the efficacy and safety of the FOLFIRI regimen with high-dose irinotecan (HD-FOLFIRI) in metastatic colorectal cancer patients. Eighty-two patients with the UGT1A1*1/*1 or the *1/*28 genotype were randomised to receive HD-FOLFIRI versus FOLFIRI. Patients with the UGT1A1*28/*28 genotype were excluded. In the experimental group, the irinotecan dose was 300 mg/m² for UGT1A1*1/*1 and 260 mg/m² for *1/*28 patients. In the control group, the dose was 180 mg/m². We analysed the overall response rate (ORR), toxicity, and survival. The ORR was significantly higher in the HD-FOLFIRI group (67.5 versus 43.6%; p = 0.001 OR: 1.73 [95% CI:1.03–2.93]). Neutropenia (17.7%), diarrhoea (5.1%), and asthenia (5.1%) were the most common grade 3–4 toxicity. No differences were observed in severe toxicity (22.5% versus 20.5%), dose reduction (22.5% versus 28.2%), or prophylactic G-CSF (17.5% versus 12.8%). No difference in survival was found. Patients with the UGT1A1*1/*1 and *1/*28 genotypes can receive high doses of irinotecan to achieve a more favourable ORR without significant adverse events.