Abstract P3-14-03: Changes in vitamin D and calcium metabolism markers in patients undergoing adjuvant chemotherapy for breast cancer

Abstract

Abstract Background:Vitamin D (VitD) insufficiency affects the majority of patients with early breast cancer (EBC). Breast cancer treatment may lead to bone loss, due to premature ovarian failure or direct chemotherapy (CT) cytotoxic effects. These increase the risk of skeletal morbidity compared to women without breast cancer history. However, even if these evidences are well described, the evolution of calcium metabolism under CT is unknown in this population with a high cure rate. We report the evolution of VitD and calcium metabolism markers in patients undergoing adjuvant CT for EBC. Material and methods: We evaluated the VitD and calcium parameters (blood calcium, phosphorus and parathormone [PTH] levels, urinary calcium excretion) in EBC patients treated with 6 cycles of adjuvant CT without high dose calcium and VitD treatment. Variables of interest were recorded at inclusion, then every 3 weeks, at each chemotherapy cycle initiation. Primary endpoint was the occurrence of a hypercalciuria during the course of adjuvant CT (between Day 1, Cycle 1 [D1C1] and Day 1, Cycle 6 [D1C6]). Results: 82 patients were evaluable for the primary endpoint. The median age was 53 years (range 20-71). CT consisted of a sequential anthracyclines and taxane regimen in 96.3% of the cases. Eleven (26.8%) patients received adjuvant trastuzumab. Most patients (66, 80.5%) presented with baseline VitD insufficiency (<30 ng/mL). Median baseline VitD level was 20.65ng/mL (range 2.9-55). Nine patients (8 VitD insufficient, 1 VitD sufficient [calcium only]) received low-dose VitD and/or calcium supplementation during the CT cycles. No baseline clinical parameter was statistically predictive of a VitD baseline insufficiency, while baseline blood calcium level was statistically predictive of a VitD baseline insufficiency (p=0.051). 94% of the patients presented with VitD insufficiency at D1C6 (median VitD level 20ng/mL; 9-39). No case of hypercalcemia was recorded. 29 patients (35.4%; 95%CI: 25.6-46.5) developed hypercalciuria between D1C1 and D1C6, none clinically significant. This percentage was not significantly different between VitD insufficient patients and the others (34.8% vs. 37.5%), nor between supplemented and not supplemented patients (37.5% vs. 34.5%). In multivariate analysis, weight and BMI were significantly associated with the occurrence of a hypercalciuria, while a trend was detected for baseline VitD (p=0.085) and albumin blood level (p=0.072). Baseline PTH level was elevated in 12.7% of the VitD insufficient patients vs. none of the patients with a normal VitD level. These percentages increased to 52.5% and 50% respectively at D1C6. Conclusions: We report here, to our knowledge, the first comprehensive study of the kinetics of VitD and calcium biomarkers during EBC adjuvant CT. This population appears highly VitD insufficient, with a compensatory elevation in blood PTH levels during the course of treatment. Hypercalciuria, while asymptomatic, is a highly prevalent abnormality in this setting, and must not be a limitation for high dose VitD supplementation. Citation Format: Jacot W, Firmin N, Touraine C, Pouderoux S, Viala M, Metge M, Rifai L, Romieu G, Roca L, Guiu S, D'Hondt V. Changes in vitamin D and calcium metabolism markers in patients undergoing adjuvant chemotherapy for breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-14-03.