# Local Ablative Treatment of the Primary Tumour in Patients With Metastatic Breast Cancer: A Retrospective Observational Study

## TL;DR

This study examines the benefits of local surgery or radiotherapy for the primary tumor in metastatic breast cancer patients who respond well to systemic treatment.

## Contribution

The study provides real-world evidence on the effectiveness of local ablative treatment in metastatic breast cancer patients with good systemic response.

## Key findings

- Patients showed excellent progression-free survival up to 60 months from diagnosis.
- Local ablative treatment was associated with a 78% probability of not relapsing at 60 months.
- Most patients had luminal breast cancer and were classified as oligometastatic.

## Abstract

Background: Metastatic disease is the cause of death in most patients with breast cancer. The potential benefits of breast surgery (i.e., mastectomy or lumpectomy) of the primary tumour in patients with metastatic breast cancer are controversial. In clinical practice, selected multimetastatic and oligometastatic patients who show a complete metabolic response to systemic treatment receive local ablative treatment (breast surgery and/or radiotherapy) of their primary tumour.

Objectives: We described the local ablative treatment of primary tumours received by patients with oligometastatic and multimetastatic breast cancer with good systemic treatment response and analysed our cohort’s progression-free survival (PFS).

Patients and methods: A retrospective, descriptive cohort study was conducted at the Consorci Sanitari de Terrassa, Spain, from March 2013 to November 2023. We included all consecutive patients aged ≥18 years with histologically confirmed metastatic breast cancer who underwent local ablative treatment after receiving systemic therapy. Oligometastatic patients presented with up to five metastatic lesions.

Results: Seventeen patients were included in our study, 16 females and one male, with a median age of 50 years (range: 26-72). Most had luminal breast cancer (9, 53%) and were classified as oligometastatic (12, 71%). Their systemic treatments followed international guidelines for each molecular subtype. The most frequently performed local ablative treatment was mastectomy with axillary lymphadenectomy (7, 41%); eight patients (47%) received local ablative treatment (radiotherapy) for metastatic lesions. The median PFS from the date of diagnosis was not reached; at 60 months, the probability of not relapsing was 92%. The median PFS from the date of local ablative treatment was also not reached; at 60 months, the probability of not relapsing was 78%.

Conclusions: In this small local series, patients with oligometastatic or multimetastatic breast cancer achieving a good response to systemic therapy and receiving local ablative treatment of their primary tumour showed excellent PFS from the date of diagnosis and from the date of local ablative treatment.