Study challenges treatment approach for rare triple-negative breast cancer

A rare form of triple-negative breast cancer may not need the same treatment approach as more common forms of the disease, a study suggests.

Researchers analysed long-term outcomes in 24 patients with adenoid cystic carcinoma of the breast, or breast ACC, diagnosed between 2000 and 2020.

Despite all patients having triple-negative breast cancer, estimated disease-specific survival was 93.3 per cent at both five and 10 years.

The study was led by researchers at The Institute of Cancer Research, London, and The Royal Marsden NHS Foundation Trust.

Lead author Dr Iseult Browne, Post-CCT is clinical research fellow at The Ralph Lauren Centre for Breast Cancer Research at The Royal Marsden Hospital, in collaboration with The Toby Robins Breast Cancer Now Research Centre at the ICR.

The researcher said: “Breast ACC is exceptionally rare, which makes conducting the large prospective clinical trials that guide management of more common breast cancers extremely challenging.

“Carefully characterised datasets with long-term follow-up are therefore particularly valuable. By studying patients treated at The Royal Marsden over a 20-year period, we were able to provide detailed long-term outcome data for a disease where evidence to guide treatment remains limited.

“We hope our findings will contribute to a better understanding of this rare form of breast cancer and help clinicians make more informed and personalised treatment decisions for patients.”

Breast ACC accounts for fewer than one in every 1,000 breast cancer cases and is usually classed as triple-negative because tumour cells lack oestrogen and progesterone receptors and HER2 expression.

More common forms of triple-negative breast cancer are often associated with aggressive disease and a higher risk of recurrence, but breast ACC appears to behave differently.

Among the 24 patients, only two had cancer detected in their lymph nodes. Chemotherapy was used specifically for breast ACC in two patients, while most were treated with surgery and radiotherapy.

Two patients died from breast ACC during the study period.

Five patients experienced a relapse. In two cases, the cancer returned more than a decade after the initial diagnosis, one after more than 11 years and another after 14 years.

The researchers said patients with breast ACC generally had a favourable long-term outlook, although the late relapses suggest longer-term follow-up may be appropriate.

Relapses appeared more frequent among patients with solid-basaloid ACC, a rare subtype, than among those with classic ACC. However, patient numbers were small and larger studies are needed to confirm the finding.

The researchers said combining clinical outcomes with molecular profiling, which examines the biological characteristics of tumours, could improve assessment of individual risk and identify potential treatment options for patients who develop advanced disease.

The findings also suggest treatment decisions should consider the specific pathology and behaviour of breast ACC rather than relying only on its triple-negative classification.