Surgical margins
In one sentence
A surgical margin is the edge of removed tissue, examined to determine whether cancer reaches that edge.
The intuition
Removing a piece of tissue creates a boundary. Pathologists mark and examine that boundary. A positive margin tells us cancer reaches the sampled cut edge; it asks whether the local removal is complete, not whether distant organs contain cancer.
How it works
For an oriented specimen, the surgeon and pathologist identify directions such as lateral or inferior. Ink marks edges. The report distinguishes invasive cancer from ductal carcinoma in situ (DCIS) at or near those edges. Separately submitted margin specimens can modify the final local interpretation; their orientation matters.
“Positive,” “close” and “negative” are not synonyms. Positive commonly means tumor on ink. A close margin reports a measured distance. What distance is sufficient depends on invasive versus in-situ disease, planned radiation and the clinical setting. A universal number cannot be applied to every report.
Completion surgery could involve another excision or mastectomy, depending on extent, anatomy, prior treatment and preferences. A margin finding does not alone choose the operation. The treating team integrates imaging, pathology and the overall local-treatment plan.
A negative margin concerns the evaluated boundary. It does not prove the absence of microscopic disease everywhere. Likewise, a positive invasive margin and negative DCIS margin can coexist. Read each component rather than compressing the report into a single “all clear” label.
Why it matters in cancer
It helps readers understand whether local removal is complete without confusing a tissue edge with distant spread.
Worked example
The main specimen has invasive cancer at its lateral edge. A new lateral specimen also has invasive cancer at its outer edge. That supports an unresolved local margin. A negative cancer-DNA blood result does not override the tissue finding.
Common confusions
- Margin status is local; it does not diagnose distant metastasis.
- Close is a measured distance, not automatically positive.
- Invasive and DCIS margins can differ, and the separately submitted specimens matter.
Related concepts
pCR and the pathology guide.
Vocabulary: pCR means pathologic complete response.
Sources and scope
General teaching, source-checked October 8, 2026. The examples are hypothetical unless a study is explicitly named. Expert and learner review remain pending.