Clinical outcomes after post-operative radiotherapy for breast cancer patients presenting with ipsilateral supraclavicular metastasis: considerations on the cranial border of irradiation field.

Background: Disease recurrence at lower neck adjacent to ipsilateral supraclavicular (SCV) region represents a concern in locally advanced breast cancer patients presenting with SCV metastasis at diagnosis. This study aims to report the outcomes following post-operative radical radiation therapy and discuss the reasonable cranial border of the irradiation field for N3c patients.

Methods: Between July 2016 and January 2022, a total of 268 patients were eligible for analysis. The endpoints included in-field and out-field cervical failures, local-regional recurrence-free survival (LRRFS), SCV recurrence-free survival (SRFS), distant metastasis-free survival (DMFS), relapse-free survival (RFS), and overall survival (OS).

Results: During a median follow-up of 37 months (range 3-89 months), 17 patients (6.3%) developed local-regional recurrence as the first recurrence event, with 13 having concomitant distant-metastasis (DM); 56 patients (20.9%) had DM alone. The 3-year rates of LRRFS, SRF, DMFS, RFS, and OS were 92.3%, 94.5%, 74.5%, 73.0%, and 90.0%, respectively. 89.2% of patients received RT with the cranial border at the top of hyoid bone, and 95.1% of patients received a boost not exceeding the level of cricoid cartilage. A total of 11 patients (4.1%) developed ipsilateral SCV failure, and 3 patients (1.1%) experienced cervical failure, including 2 in-field failures and 1 out-field failure. Neoadjuvant systemic therapy (NST) was administered to 234 patients (87.3%). In the multivariate analysis, non-ypN0, triple-negative subtype and cT4 at diagnosis were predictors of worse SRFS and RFS in NST subgroup.

Conclusion: Our findings suggest that radical RT with cranial border of irradiation field at the hyoid bone level lead to excellent local-regional control, and out-field cervical failure was rare. The irradiation field might not extend to mastoid process.