59P - The impact of site of metastasis on overall survival in indigenous and non-indigenous patients of Western Australia with breast cancer

Background

Indigenous women with breast cancer (BrCa) have markedly higher mortality then non-Indigenous women. Here, we examine the impact of site of metastasis on overall survival (OS) in women with breast cancer by indigenous status.

Methods

We retrospectively examined data from WA cancer registry from 2001 to 2016 with metastatic BrCa by indigenous status. Cases with confirmed location of metastatic disease were analysed and divided into groups of bone, liver, brain, lung, gastrointestinal (GI)/genitourinary (GU), contralateral breast (CBr) and skin metastasis. We performed a univariate and linear regression analysis to determine the impact of metastasis site on OS. Kaplan-Meier, Chi-square, Mann-Whitney analysis were done.

Results

A total of 152 patients were studied, 39% (n=60) were indigenous vs 61% (n=92) non-indigenous. Inferior median OS for indigenous group 34 vs 51 months in non-indigenous group, p=0.015. Indigenous group had higher rates of metastasis to bone 61% vs 40% (p=0.014), lung 41% v 25% (p=0.031), liver 41% v 23% (p=0.021) when compared to non-indigenous patients. The GI/GU metastasis was higher in non-indigenous group 32% v 15% (p=0.015) in indigenous group. There were no significant differences in rate of relapse at the local, CBr, brain, spleen, non-axillary LN nor skin (p>0.05). The bone metastasis was most common in luminals, liver and lung metastasis were frequent in luminal B and Her2+ subtypes. Brain metastasis was most frequent in HER2+. Indigenous cohort had more HER2+, luminal B and TN’s than non-indigenous but this was non-significant, p < 0.467. The multiple linear regression in both groups to predict OS for site-specific metastasis was non-significant with p-value 0.067 and R² of 0.097, explaining slight variability of OS by sites of metastasis. After adjustment, only brain metastasis had significant regression weights, but further analysis shown non-significant effect on OS with p=0.072 and an R² of 0.021.The group with brain metastasis had OS of 38 vs 52 months with no brain metastasis, p=0.072.

Conclusions

The indigenous group had inferior survival and higher rates of relapse to bones and viscera. A larger prospective study is needed to establish links of site of metastasis and OS.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Dr Azim Khan.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.