Larger surgical margins improved survival in localized Merkel cell carcinoma

Among patients with localized Merkel cell carcinoma, surgical margins larger than 1 cm improved survival regardless of factors such as tumor subsite and receipt of adjuvant chemotherapy, according to a study.

“Current recommendations regarding the size of local excision (LE) margins for Merkel cell carcinoma (MCC) have not been well established,” Neal Andruska, MD, PhD, of the department of radiation oncology at Washington University School of Medicine in St. Louis, and colleagues wrote.

The objective of the multicenter retrospective cohort study was to determine if larger clinical LE margins, along with adjuvant radiotherapy, would yield improved overall survival (OS) in a cohort of 6,156 patients with localized MCC.

Eligible participants had stage I or stage II disease and underwent excision between Jan. 1, 2004, and Dec. 31, 2015.

Along with OS, net survival served as the primary outcome measure.

Patients were diagnosed at a median age of 77 years, and the cohort was 40.6% women.

Results showed an association between LE margins greater than 1 cm and improved OS (HR = 0.88; 95% CI, 0.81-0.95; P<.001) compared with margins smaller than that threshold. This survival improvement was independent of tumor subsite.

When patients were assessed 5 years after the procedure, net survival rates were 76.7% for patients with LE margins of 1 cm or smaller and 89.8% for those with margins larger than 1 cm (P <.001).

Further stratification of LE margins into subgroups showed that, compared with margins less than 1 cm, margins between 1.1 cm and 2 cm (HR = 0.87; 95% CI, 0.76-0.99; P=.047) and those larger than 2 cm (HR = 0.84; 95% CI, 0.72-0.98; P=.03) were associated with improved OS.

The researchers defined patients with less aggressive disease as those who were immunocompetent with tumors 1 cm or less, no lymphovascular invasion and negative pathologic margins, according to the findings. In those patients with LE margins larger than 1 cm, improvements in OS were reported (HR = 0.87; 95% CI, 0.78-0.97; P=.01).

Adjuvant radiotherapy improved OS not only in patients with larger LE margins (HR = 0.87; 95% CI, 0.76-0.98; P=.03), but in those from all three LE margin subgroups.

Comparable OS was reported among patients who received adjuvant radiotherapy and had LE margins of 1 cm or smaller (HR = 0.81; 95% CI, 0.76-0.98; P<.001) and those with no adjuvant radiotherapy and LE margins larger than 1 cm (HR = 0.80; 95% CI, 0.71-0.89), according to the results.

“The study’s findings support the use of LE margins of 1.1 cm to 2 cm and suggest that adjuvant radiotherapy may be important to consider for the treatment of all patients with stage I to stage II MCC regardless of LE margin status,” the researchers wrote.