Breast Cancer Metastatic – Rapid Oral Abstract Session

The first daily highlight in breast cancer at this ASCO 2025 is presented by Dr Laure-Anne Teuwen (University Hospital Antwerp), who has selected three particularly interesting presentations from the rapid oral abstract session on metastatic breast cancer.

A first discussed study explored the use of AI software to aid in interpreting HER2 immunohistochemistry staining, particularly in the ultra-low and low categories, which are challenging to assess and often misclassified. They used 20 slides analysed by 105 pathologists in three phases: baseline scoring, post-training scoring, and AI-assisted scoring. AI assistance boosted concordance from 0.5 to 0.8 and accuracy from 89% to 96%. Misclassification of HER2 zero improved by 24%. However, the AI platform’s training and development details weren’t provided. Variability in slide staining across different laboratories could limit the generalisability of AI. The pathologists’ training likely influenced results too, as scores after training and AI use were compared to baseline. More prospective validation trials are needed before adopting this AI tool widely.

A retrospective multicenter US study investigated the safety of re-challenging with T-DXd after T-DXd-induced interstitial lung disease (ILD). Out of 1,500 patients treated with T-DXd for various cancers, 10% developed ILD, with a 0.5% mortality rate. Fifty-nine patients with grade 1 ILD were eligible for re-challenge, and 44 underwent it. Half had residual CT abnormalities, and most were re-challenged at a reduced dose. Of these, 27% developed a second ILD, typically mild (grade 1 or 2). Three patients were re-challenged again and did well. Additionally, 19 patients with grade 2 ILD were re-challenged against guidelines, and 16% developed more severe ILD (grade 3–4). This study supports safe re-challenge in grade 1 ILD cases but cautions against it in grade 2. It provides valuable guidance for clinical decisions on T-DXd re-challenge.

The MINI trial explored a chemo-free regimen in HER2+, HR+ metastatic breast cancer using ribociclib, letrozole, and trastuzumab. It was a phase Ib/II study enrolling pre- and postmenopausal patients, mostly without prior metastatic treatment. Phase I determined that 600 mg of ribociclib was the dose for Phase II. Phase II involved 77 patients, allowing for prior neoadjuvant or adjuvant therapy if completed well before enrollment. Median PFS was an impressive 30.2 months. Median OS was not reached. The most common grade 3/4 adverse events were neutropenia, itching, and nausea. Overall, the results are promising for a chemo-free approach. Further phase 3 trials will be crucial to confirm these findings.