Stereotactic Body Radiotherapy (SBRT) for Breast Cancer Spinal Metastases is Associated with Low Rates of Long-Term Local Failure (LF) and Vertebral Compression Fracture (VCF) Independent of Molecular Status

PURPOSE/OBJECTIVE(S)

There is limited outcome data specific to breast cancer spinal metastases following spine SBRT. This study aims to report outcomes specific to breast cancer spinal metastases receiving spine SBRT and determine the implication of biomarker status.

MATERIALS/METHODS

We have been maintaining a prospective database since the inception of the spine SBRT program. A retrospective review identified 168 breast cancer patients with 409 spinal segments treated with spine SBRT between January 2008 and January 2023. Molecular subtypes were grouped based on luminal A, luminal B, basal, and HER2 enriched. Patients were followed with q3-monthly full-spine MRI and a clinical assessment. The primary endpoint was MRI-based local failure (LF), and secondary endpoints were overall survival (OS) and vertebral compression fracture (VCF).

RESULTS

The median follow-up was 33 months (range, 3.3-123 months). Amongst the 168 patients, the majority were ECOG 0 or 1 (95%), neurologically intact (94%), polymetastatic (74%), and either luminal A (71%) or luminal B (8%). A total of 17% of patients were HER2+ve versus 83% HER2-ve. Of 409 treated segments the majority (76%) had no prior radiation or surgery (de novo), were SINS stable (60%), had either no or low-grade epidural disease (86%) and treated with 24-28 Gy in 2 fractions (73%). The LF and OS rates at 1, 3, and 5 years were 5%, 11%, and 14%, respectively, and 91%, 65%, and 45%, respectively, independent of molecular subtype on univariate analyses. The cumulative risk of VCF at 2 and 5 years was 7% and 10%, respectively.

CONCLUSION

We observe, in the largest breast cancer spine cohort to date, excellent long-term local control rates independent of molecular sub-group, and acceptable VCF rates.

Does adjuvant radiation therapy benefit women with small mammography-detected breast cancers?

BACKGROUND

Women with small nonpalpable breast tumours have an excellent prognosis. The benefit of radiotherapy in this group of low-risk women is unknown.

METHODS

A cohort of 1595 women with stages i-iii invasive breast cancer treated with breast-conserving surgery were followed for local recurrence. Using t-tests, baseline demographic data and tumour characteristics were compared for the women who had palpable (n = 1023) and mammography-detected (n = 572) breast cancers. The 15-year actuarial risk of local recurrence was estimated using a Kaplan-Meier method, stratified for adjuvant radiation therapy (yes or no), tumour palpability (palpable or not), and tumour size (≤1 cm or >1 cm). Hazard ratios (hrs) and 95% confidence intervals (95% cis) were calculated using a multivariate Cox regression model. Results were considered statistically significant if 2-tailed p values were less than 0.05.

RESULTS

Among women with a nonpalpable tumour, the 15-year actuarial rates of local recurrence were, respectively, 13.9% and 18.3% for those treated and not treated with adjuvant radiation therapy (hr: 0.65; 95%ci: 0.40 to 1.06; p = 0.08). Among women with small nonpalpable breast cancers (≤1.0 cm), the rates were 14.6% and 13.4% respectively (p = 0.67). The absolute reduction in 15-year local recurrence was 11.0% for women with palpable tumours.

CONCLUSIONS

Our results suggest that women with small (<1 cm) screen-detected nonpalpable breast cancers likely derive little benefit from adjuvant radiotherapy; however, an adequately powered randomized trial would be required to make definitive conclusions.