Association of triple-negative breast cancer with decreased T score of femoral neck at the time of osseous metastasis.

Abstract

e13132 Background: While agents are administered when indicated, skeletal vulnerability may vary ; however, molecular subtype-specific differences in bone mineral density(BMD) in patients at the time of bony metastasis yet to be clearly delineated. Methods: This retrospective cohort study included patients with breast cancer with bone metastasis treated between January 2000 and December 2022. The median follow-up period was 36 months or longer. T-scores of femoral neck and lumbar spine at the time of bone metastasis were the primary skeletal outcome, and serum 25-hydroxyvitamin D and pyridinoline were analyzed as representative bone metabolism markers. Multivariable linear regression was used to evaluate factors associated with BMD. Results: A total of 184 patients with bone metastasis were analyzed (luminal A, n = 104; luminal B, n = 41; HER2-enriched, n = 16; TNBC, n = 23). The interval from initial diagnosis to bone metastasis differed significantly by subtype, with luminal subtypes showing the longest latency and TNBC the shortest. Femoral neck T-scores varied significantly across subtypes, with TNBC demonstrating the lowest mean values, whereas lumbar T-scores did not differ significantly. Biochemical markers of bone metabolism was subtype-specific. TNBC patients had lower serum 25-hydroxyvitamin D levels and higher pyridinoline levels, consistent with increased bone turnover. The prevalence of osteoporosis, vitamin D deficiency, and a composite high-risk skeletal phenotype was highest in TNBC compared with others. In multivariable analyses adjusting for age, body mass index, and treatment-related factors, TNBC remained independently associated with lower femoral neck T-scores. Conclusions: Bone mineral density differ substantially by subtype in breast cancer at the time of bone metastasis. TNBC is associated with pronounced skeletal vulnerability, characterized by reduced bone mineral density and adverse bone metabolic profiles, independent of endocrine therapy exposure. Multivariable linear regression analysis of factors associated with femoral bone mineral density. Variable Model 1 β (95% CI) Model 2 β (95% CI) Model 3 β (95% CI) Luminal B −0.18 (−0.45 to 0.08) −0.15 (−0.42 to 0.11) −0.12 (−0.38 to 0.14) HER2-enriched 0.22 (−0.12 to 0.56) 0.19 (−0.15 to 0.53) 0.17 (−0.16 to 0.50) TNBC −0.63 (−0.94 to −0.32) −0.58 (−0.89 to −0.27) −0.52 (−0.83 to −0.21) Age (per year) −0.03 (−0.04 to −0.02) −0.03 (−0.04 to −0.02) −0.03 (−0.04 to −0.02) Body mass index (kg/m²) 0.07 (0.03 to 0.11) 0.06 (0.02 to 0.10) 0.05 (0.01 to 0.09) Postmenopausal status −0.31 (−0.58 to −0.05) −0.28 (−0.54 to −0.02) −0.24 (−0.50 to 0.01) Aromatase inhibitor use −0.26 (−0.49 to −0.03) −0.22 (−0.45 to 0.01) −0.18 (−0.40 to 0.04) Model 1 included molecular subtype only. Model 2 was adjusted for age and body mass index. Model 3 was additionally adjusted for menopausal status and aromatase inhibitor use.