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Narrow DCIS Margins May Not Always Warrant Reexcision
An ancillary analysis found less than 2-percentage-point differences in 10-year recurrence across margin thresholds, with no statistically significant adjusted association.
To evaluate the association between margin width and ipsilateral breast tumor recurrence (IBTR) in postmenopausal patients with hormone receptor-positive ductal carcinoma in situ (DCIS).
Approach:
Study Design: Ancillary analysis of prospectively collected margin data from the phase 3 NRG Oncology/National Surgical Adjuvant Breast and Bowel Project B-35 trial.
Patient Population: 3,104 postmenopausal patients with hormone receptor-positive DCIS and tumor-free margins enrolled from January 2003 to June 2006.
Margin Analysis: Evaluated IBTR using protocol-defined margin groups of <1 mm vs ≥1 mm and guideline-based groups of <2 mm vs ≥2 mm.
Statistical Methods: Calculated 10-year cumulative incidence while accounting for competing risks and adjusted for age, endocrine therapy assignment, and tumor size.
Key Findings:
10-year cumulative incidence of IBTR was 5.6% for margins <1 mm and 4.0% for margins ≥1 mm (unadjusted difference significant).
In the 2-mm analysis, IBTR was 5.3% for margins <2 mm and 3.8% for margins ≥2 mm (unadjusted difference significant).
After adjustment, margin width was not statistically significantly associated with IBTR at either threshold.
Tumor size was associated with recurrence; tumors ≥1 cm had approximately twice the adjusted hazard of IBTR compared to smaller tumors.
65% of patients completed 5 years of endocrine therapy, with no difference in adherence by margin group.
Interpretation:
Limitations:
Margin width was not randomized and no intervention based on margin width was included.
Margin status assessed by local pathologists without real-time central review.
Excluded patients included those with positive margins and missing pathology forms.
Tumor size was estimated in a significant portion of patients.
Analysis did not address premenopausal patients or hormone receptor-negative DCIS.
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