(ChemotherapyAdvisor) – Patients undergoing breast-conserving therapy for triple-negative, HER2, and luminal-B breast cancers suffer higher rates of subsequent brain metastasis than do patients with other breast cancer subtypes, report authors of a study published in Breast Cancer Research and Treatment.

The risk of brain metastasis after breast-conserving therapy “varies significantly by subtype,” reported Nils D. Arvold, MD, Department of Radiation Oncology, Dana-Farber/Brigham & Women’s Cancer Center, Harvard Medical School, in Boston, Massachusetts, and coauthors.

The risk of brain metastasis following breast-conserving therapy for early-stage breast cancer remains low, “even in an era of widespread systemic therapy,” they noted. Overall 5-year cumulative incidence of brain metastasis was 1.7%, and the rate among patients with luminal-A breast cancer was 0.1%.

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But brain metastasis rates were higher for some subtypes: 3.3% for luminal B, 3.2% for luminal-HER2, 3.7% for HER2 — and 7.4% for triple-negative breast cancer, the authors reported. Median brain metastasis tumor size was 15 mm overall, with larger median tumor diameters in patients with triple-negative and luminal-B tumors (triple negative, 27 mm; luminal B, 16 mm). 

The study included 1,434 consecutive patients diagnosed with stage I/II invasive breast cancer who underwent breast-conserving therapy from 1997 to 2006. Most (91%) received adjuvant systemic therapy. Median follow-up was 85 months.

“Median time from DM (distant metastasis) to BM (brain metastasis) was 12.8 months but varied by subtype, including 7.4 months for TN, 9.6 months for luminal B, and 27.1 months for HER2,” the authors reported.

Median time from breast cancer diagnosis to brain metastasis detection was 51.4 months (7.6–108 months) but was longer among patients with luminal subtype tumors compared to patients with other breast cancer subtypes (61.4 months vs. 34.5 months, P=0.0002). 

Brain metastasis was more likely among women diagnosed at younger age (P <0.0001), with lymph node involvement (P <0.0001), grade 3 tumors (P <0.0001), hormone receptor-negative tumors (P =0.006) or HER2-positive tumors (P=0.01).

“(W)omen with luminal B and triple-negative tumors may benefit from routine brain MRI surveillance after diagnosis of extracranial distant metastasis,” they wrote. “This may decrease the number of women presenting with symptomatic and/or large brian metastases and increase treatment options.”