Discrepancies between dihydropyrimidine dehydrogenase phenotyping and genotyping: What are the explanatory factors?

AIM: Dihydropyrimidine dehydrogenase (DPD) deficiency can be detected by phenotyping (measurement of plasma uracil [U], with U ≥ 16 µg/L defining a partial deficiency) and/or by genotyping (screening for the four most frequent DPYD variants). We aimed to determine the proportion of discrepancies between phenotypic and genotypic approaches and to identify possible explanatory factors. METHODS: Data from patients who underwent both phenotyping and genotyping were retrospectively collected. Complementary genetic analyses (genotyping of the variant c.557A>G and DPYD sequencing) were performed for patients with U ≥ 16 µg/L without any common variants. The characteristics of patients classified according to the congruence of the phenotyping and genotyping approaches were compared (Kruskal-Wallis test), and determinants of U levels were studied in the whole cohort (linear model). RESULTS: Among the 712 included patients, phenotyping and genotyping were discordant for 12.5%, with 63 (8.8%) having U ≥ 16 µg/L in the absence of a common variant. Complementary genetic investigations marginally reduced the percentage of discrepancies to 12.1%: Among the nine additional identified variants, only the c.557A>G variant, carried by three patients, had been previously reported to be associated with DPD deficiency. Liver dysfunction could explain certain discordances, as ASAT, ALP, GGT and bilirubin levels were significantly elevated, with more frequent liver metastases in patients with U ≥ 16 µg/L and the absence of a DPYD variant. The impact of cytolysis was confirmed, as ASAT levels were independently associated with increased U (p < 0.001). CONCLUSION: The frequent discordances between DPD phenotyping and genotyping approaches highlight the need to perform these two approaches to screen for all DPD deficiencies.

Severe toxicity of capecitabine in a patient with DPD deficiency after a safe FEC-100 experience: why we should test DPD deficiency in all patients before high-dose fluoropyrimidines.

We report the case of a 44-year-old patient who experienced severe toxicity while being treated with capecitabine at standard dose for metastatic breast cancer. As the patient had already received 5-FU within the FEC protocol (5-FU 500 mg/m2, epirubicin 100 mg/m2, and cyclophosphamide 500 mg/m2) 10 years ago without experiencing any severe adverse event, no DPD deficiency testing was performed before capecitabine treatment. Nevertheless, she experienced severe diarrhea and grade 2 hand-foot syndrome from the first cycle, forcing her to stop the treatment. Phenotypic and genotypic investigation of DPD activity revealed that the patient had a partial deficiency and had therefore been exposed to a higher risk of developing severe toxicities on fluoropyrimidines. This case proves that tolerance to low-dose fluoropyrimidines does not preclude DPD deficiency and the occurrence of severe toxicities if higher doses of fluoropyrimidines are used as a second-line treatment. It emphasizes the role of DPD phenotyping testing based on uracilemia in patients scheduled for fluoropyrimidine drugs, even if previous courses with low-dose 5-FU were safely administered.

New DPYD variants causing DPD deficiency in patients treated with fluoropyrimidine.

PURPOSE: Several clinical guidelines recommend genetic screening of DPYD, including coverage of the variants c.1905 + 1G>A(DPYD*2A), c.1679T>G(DPYD*13), c.2846A>T, and c.1129-5923C>G, before initiating treatment with fluoropyrimidines. However, this screening is often inadequate at predicting the occurrence of severe fluoropyrimidine-induced toxicity in patients. METHODS: Using a complementary approach combining whole DPYD exome sequencing and in silico and structural analysis, as well as phenotyping of DPD by measuring uracilemia (U), dihydrouracilemia (UH2), and the UH2/U ratio in plasma, we were able to characterize and interpret DPYD variants in 28 patients with severe fluoropyrimidine-induced toxicity after negative screening. RESULTS: Twenty-five out of 28 patients (90%) had at least 1 variant in the DPYD coding sequence, and 42% of the variants (6/14) were classified as potentially deleterious by at least 2 of the following algorithms: SIFT, Poly-Phen-2, and DPYD varifier. We identified two very rare deleterious mutations, namely, c.2087G>A (p.R696H) and c.2324T>G (p.L775W). We were able to demonstrate partial DPD deficiency, as measured by the UH2/U ratio in a patient carrying the variant p.L775W for the first time. CONCLUSION: Whole exon sequencing of DPYD in patients with suspicion of partial DPD deficiency can help to identify rare or new variants that lead to enzyme inactivation. Combining different techniques can yield abundant information without increasing workload and cost burden, thus making it a useful approach for implementation in patient care.

[Importance of hyperthermic intraperitoneal chemotherapy (HIPEC) in ovarian cancer]. / Place de la chimio-hyperthermie intrapéritonéale (CHIP) dans le cancer de l'ovaire.

Hyperthermic intraperitoneal chemotherapy (HIPEC) represents a new treatment strategy aimed to improve outcome of patients with advanced ovarian cancer. Based on theoretical and experimental basis, HIPEC should stand as an effective treatment for ovarian cancer. Literature review reveals a number of different experiences on feasibility of this technique, but scientific evidence of current studies remains poor. Much more research is still required to elucidate unanswered questions. Before this technique can be routinely used, some controversial aspects have to be defined: which drug is the best to deliver and at what temperature, is it necessary to use mono- or poly-chemotherapy regimens, which is the time-point for HIPEC in the natural history of ovarian cancer: at front-line therapy, at interval debulking following initial neo-adjuvant chemotherapy, at consolidation following front-line therapy, or at the time of recurrence. Nevertheless, we must not forget that the most important issue in ovarian cancer prognosis is maximal cytoreductive surgery, with no residual disease at completion of initial surgery.

Pharmacokinetics of oxaliplatin during open versus laparoscopically assisted heated intraoperative intraperitoneal chemotherapy (HIPEC): an experimental study.

BACKGROUND: Hyperthermic intraperitoneal chemotherapy (HIPEC) is being evaluated for patients with minimal residual or no residual disease after primary surgery and chemotherapy for stage III ovarian carcinoma. The technical feasibility of the laparoscopic approach for HIPEC has been demonstrated in a previous study. An experimental study on the porcine model was carried out to compare oxaliplatin pharmacokinetics during a laparoscopic-assisted procedure versus the coliseum technique for HIPEC. METHODS: Adult pigs received an HIPEC procedure that was based on 460 mg/m(2) of oxaliplatin over 30 minutes with a perfusate heated at 41 degrees C to 43 degrees C. The HIPEC drains were placed in the upper and lower quadrants of the abdomen. Peritoneal fluid and blood samples were collected every 10 minutes during the procedure, and the pharmacokinetics of oxaliplatin was studied. RESULTS: Two groups of 10 adult pigs were studied. All the procedures were successfully completed with an adequate intra-abdominal temperature and distribution. No major technical problems were encountered. At the end of the HIPEC, 41.5% of the molecule was absorbed in the laparoscopic group compared with 33.4% in the laparotomy group (P = .0543). Peritoneal oxaliplatin half-life (T((1/2))) was significantly faster in the laparoscopic procedure (median, 37.5 vs. 59.3 minutes, P = .02). The area under the curve ratio of peritoneal to plasma reflects a more important oxaliplatin crossing through the peritoneal barrier in the laparoscopic procedure (ratio, 16.4 in the closed procedure vs. 28.1 in the open one; P = .03). CONCLUSIONS: This study confirms the technical feasibility and reliability of the laparoscopic approach for HIPEC, and it extends knowledge concerning peritoneal drug absorption. Oxaliplatin absorption is far higher with laparoscopy in terms of time course in peritoneal perfusion. Clinical application in selected patients may be expected after further experimental investigation designed to define the adequate drug dosage.

[Interest of cystatin C for individual dosing of anticancer drugs cleared by the kidneys]. / Intérêt de la cystatine C pour l'adaptation de posologie des médicaments anticancéreux à élimination rénale.

Cystatin C is a protein freely filtered in the renal glomerulus, then reabsorbed and completely metabolised within the tubular cells. The possibility to predict the clearance of compounds eliminated by the kidneys (and then to control their interindividual variability) was evaluated for two cytotoxic drugs (carboplatin and topotecan) in adults and EDTA (ethylene diamine tetraacetic acid), a compound used to determine the glomerular filtration rate in children. The population pharmacokinetic approach based on NONMEM program was used. For each of the three compounds, the cystatin C serum level was better predictive of clearance than that of creatinine. Moreover, for carboplatin and EDTA, the best equation between clearance and patients' characteristics included both cystatin C and creatinine level. A generalisation of cystatin C assay would contribute to standardise the clinical practices in Oncology.