Pre-clinical and clinical data indicate two different subtypes of HER2 positive breast cancers: HR+HER2+ and HR-HER2+, with distinct clinicopathology and behaviour. We further explored these potential differences, including the pattern of relapse and survival, using data from a HER2+MBC registry.
The TABITHA registry is prospectively collecting data on patients with HER2+ MBC across multiple sites in Australia. Comparing patients with HER2+HR- tumours with patients with HER2+HR+tumors, we examined patient demographics, tumour size, nodal status, grade, site of metastasis, type of presentation (de novo versus recurrent metastatic disease), progression free survival (PFS), and overall survival (OS).
One hundred patients with HER2+ MBC included in TABITHA database were enrolled between 24/02/2015 and 8/8/2017.Most patients (63%) presented with relapsed disease. Sixty patients (60%) had HR+HER2+ tumours and forty patients (40%) had HR-HER2+ tumours. Compared with patients with HR+HER2+, the patients with HR-HER2+ tumours were significantly more likely to present with visceral disease, commonly involving the CNS (p=0.01) and the lung (p=0.03).Ten out of 25(62.5%) patients with HR-HER2+ MBC who presented with relapsed disease, relapsed within CNS, whilst only one out of 15 of patients (6.7%) with de novo HR-HER2+ MBC had CNS involvement. Median PFS was significantly longer for patients with HR+HER2+tumors than for patients with HR-HER2+tumors (19.4 months vs. 16.2 months, p=0.023).Similarly, the median OS for patients with HR+HER2+ was significantly greater (not reached vs. 33.6 months in patients with HR-HER2+ tumours) (p=0.013).Patients who had received anti- HER2 therapy in the adjuvant setting had a shorter median survival than treatment naive patients (42.8 months vs. not reached, p=0.048).
This study suggests significant clinicopathologic and outcome differences between the two cohorts of HER2+ MBC based on HR status. Further work will be done to expand on these results.