Pharmacokinetics of Trastuzumab After Subcutaneous and Intravenous Administration in Obese Patients.

Background: Subcutaneous trastuzumab (T-SC) administration does not allow the historical target concentration of 20 µg/mL for efficacy to be reached, from the start of treatment in patients with a body mass index (BMI) >30 kg/m2. Objectives: To analyze the influence of the strategy of dosification (fixed vs adjusted patient's body weight dose) on the initial minimum plasma concentration (Cmin) of trastuzumab in obese patients. Methods: This was an observational, prospective study, which included patients with HER2-positive nonmetastatic breast cancer treated with trastuzumab. The determination of the Cmin of trastuzumab was performed on day +21 of the first cycle using the ELISA technique. Patients were stratified according to the strategy of dosification and BMI. Results: A total of 50 patients were included; 16 patients received the drug intravenously and 34 in a fixed dosage subcutaneous (T-SC) regimen. The proportion of patients who achieved an adequate plasma concentration since the beginning of treatment was significantly higher when the drug was administered intravenously (93.8% vs 67.6%, P = 0.042). These differences are especially greater in T-SC patients with BMI >30 kg/m2, with only 20% of patients exceeding the pharmacokinetic target. Conclusion and Relevance: Our study suggests that trastuzumab SC fixed dose of 600 mg is not equivalent to IV administration, especially in obese patients. An adequate trastuzumab exposure in this population needs patient weight-adjusted IV dosage in the first administration. The clinical relevance of these findings remains to be elucidated, and further research, including larger controlled trials, is warranted.

Influence of Anthropometric Characteristics in Patients With Her2-Positive Breast Cancer on Initial Plasma Concentrations of Trastuzumab.

BACKGROUND: Plasma concentrations of trastuzumab <20 µg/mL in patients with gastric cancer are associated with reduced progression-free and overall survival. In breast cancer treatment, this relationship has not yet been studied, but a suboptimal pharmacodynamic exposure to trastuzumab could be a reason for therapeutic failure of treatment of HER2-positive breast cancer. OBJECTIVE: The objective of the present study was to determine the proportion of nonmetastatic HER2-positive breast cancers that do not reach a minimum plasma concentration ( Cmin) of 20 µg/mL after first drug administration, established as therapeutically effective in clinical trials. The secondary objective was to identify the physiological and anthropometric characteristics that determine interindividual pharmacokinetic variability. METHODS: Serum concentrations of trastuzumab were assessed by ELISA on day 1 of the second cycle before administration of the second dose ( Cmin). RESULTS: Of 19 patients included, 9 (47.4%) had a mean Cmin of 19.0 µg/mL (±12.1) after the first administration. Body mass index (BMI) and weight was the main variable that determined the achievement of therapeutic levels after the first administration. Thus, the proportion of patients reaching the target concentration was 89% when BMI was ≤30 kg/m2 but only 11% when BMI was >30 kg/m2 ( P < 0.01). CONCLUSIONS: The standard dose of 600 mg subcutaneous trastuzumab did not ensure adequate pharmacodynamic exposure from the first administration in 52% of patients, with weight and BMI being related to the plasma levels obtained.

TTCC-2019-02: real-world evidence of first-line cetuximab plus paclitaxel in recurrent or metastatic squamous cell carcinoma of the head and neck.

Objectives: The aim of this study was to confirm the efficacy of the ERBITAX scheme (paclitaxel 80 mg/m2 weekly and cetuximab 400 mg/m2 loading dose, and then 250 mg/m2 weekly) as first-line treatment for patients with recurrent/metastatic squamous cell carcinoma of the head and neck (SCCHN) who are medically unfit for cisplatin-based (PT) chemotherapy. Materials and methods: This retrospective, non-interventional study involved 16 centers in Spain. Inclusion criteria were to have started receiving ERBITAX regimen from January 2012 to December 2018; histologically confirmed SCCHN including oral cavity, oropharynx, hypopharynx, and larynx; age ≥18 years; and platinum (PT) chemotherapy ineligibility due to performance status, comorbidities, high accumulated dose of PT, or PT refractoriness. Results: A total of 531 patients from 16 hospitals in Spain were enrolled. The median age was 66 years, 82.7% were male, and 83.5% were current/former smokers. Patients were ineligible to receive PT due to ECOG 2 (50.3%), comorbidities (32%), PT cumulative dose ≥ 225 mg/m2 (10.5%), or PT refractoriness (7.2%). Response rate was 37.7%. Median duration of response was 5.6 months (95% CI: 4.4-6.6). With a median follow-up of 8.7 months (95% CI: 7.7-10.2), median PFS and OS were 4.5 months (95% CI: 3.9-5.0) and 8.9 months (95% CI: 7.8-10.3), respectively. Patients treated with immunotherapy after ERBITAX had better OS with a median of 29.8 months compared to 13.8 months for those who received other treatments. The most common grade ≥ 3 toxicities were acne-like rash in 36 patients (6.8%) and oral mucositis in 8 patients (1.5%). Five (0.9%) patients experienced grade ≥ 3 febrile neutropenia. Conclusion: This study confirms the real-world efficacy and tolerability of ERBITAX as first-line treatment in recurrent/metastatic SCCHN when PT is not feasible. Immunotherapy after treatment with ERBITAX showed remarkable promising survival, despite potential selection bias.