Exploring the relationships between hormone receptor, HER2 status, and bone involvement in the first distant metastases of in Chinese breast cancer patients who lacked HER2 targeted therapy.

Background: This retrospective study explored the relationship between hormone receptor (HR), human epidermal growth factor receptor 2 (HER2) status, and bone involvement in the first distant metastases (DM) of Chinese breast cancer (BC) patients who lacked the HER2 targeted therapy. Such therapy was rarely received due to its lag approval or high cost in China compared with the developed countries.

Methods: All eligible women with primary unilateral stage I - III BC and first DM diagnosed in 2008-2018 at one cancer center were identified for enrollment. Based on chart records, a full or no/partial compliance status of endocrine therapy (ET) was assigned for HR-positive patients. Multivariate logistic regression was used to estimate the adjusted odd ratio (aOR), its 95%CI and p value.

Results: Four hundred eighteen patients had an average age of 50.7 years and median disease-free survival of 27.1 months at DM. Bone, lung, liver and brain metastasis rates in patients were 55.7%, 34.7%, 33.0% and 8.1%, respectively. Compared to HR-negative patients, HR-positive patients with the full and non/partial compliance of ET were significantly associated with higher risk of bone involvement with an aOR of 2.329 (1.316 - 1.741, p = 0.004) and 2.317 (1.330 - 4.036, p = 0.003), respectively. No difference of such risk was found between the two groups of ET compliance (p = 0.984) nor between HER2-negative and HER2-positive patients (aOR 0.827, p = 0.431). Stratified analyses further indicated that HR-positive was associated with bone involvement only in HER2-negative BC patients (p = 0.006-0.015).

Conclusions: HR-positive tumors are significantly associated with bone involvement in HER2-negative metastatic BC patients. ET does not appear to impact this association. HER2 status per se is not associated with such risk.