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Purpose:
Management of positive margins after non-melanoma skin cancer (NMSC) excision is debated in the literature. Our goal was to determine the rate of residual tumor in re-excised NMSC specimens after previous excision with positive margins. Further, we sought to determine potential factors that could predict a true-positive margin.
Methods:
An IRB-approved retrospective review was conducted examining all patients with skin neoplasm excision CPT-codes over a 5-year period at a single institution. A total of 2,886 patients were evaluated; 185 patients met inclusion criteria of NMSC excision with positive margins by permanent evaluation and subsequent re-excision for clearance of tumor. Variables collected include: age, gender, history of previous skin cancer, location of tumor, skin cancer subtype (basal vs. squamous), surface area of initial excision and second excision, depth of initial excision and second excision, and time interval between first and second excisions.
Results:
103 patients (56%) with positive margins on initial excision had no evidence of residual cancer upon re-excision. The most common locations for lesions with positive margins on initial excision were on the face (53%, n=98) followed by the extremities (19.5%, n=36). Gender and age were not associated with a positive re-excision (p>0.05) (Table 1). Patients with a previous history of basal cell carcinoma were more likely to have a true-positive margin (p= 0.03) (Table 1). Larger secondary excisions were more likely to harbor residual cancer upon re-excision (6.26cm², p=0.01) (Table 1). Location of lesion did not predict positive re-excision (Table 2).
Table 1. Patient Demographic and Excision Characteristics

	Positive Re-excision (n=82)	Negative Re-excision (n=103)	p value
Female	34 (41.5%)	35 (34%)	0.30
Age	72.66 ± 14.5	71.84 ± 12.7	0.69
Hx of Ca: BCC	33 (40.2%)	25 (25.2%)	0.03
Hx of Ca: SCC	11 (13.4%)	17 (16.5%)	0.56
Cm2 First	3.34 ± 5.52	2.58 ± 3.19	0.27
Cm2 Second	6.26 ± 11.79	2.68 ± 4.52	0.01
Depth First	.435 ± .309	.479 ± .702	0.60
Depth Second	.549 ± .457	.468 ± .270	0.14

Table 2. Location of NMSC

	Positive Re-excision (n=82)	Negative Re-excision (n=103)	p value
Face	40 (48.8%)	58 (56.3%)	0.31
Scalp	8 (9.8%)	8 (7.8%)	0.63
Neck	5 (6.1%)	4 (3.9%)	0.51
Trunk	11 (13.4%)	15 (14.6%)	0.82
Extremities	18 (22%)	18 (17.5%)	0.45

Conclusion:
The absence of residual tumor after re-excision of specimens with positive margins is 56%; higher than that reported in the literature. Patients with a history of basal cell carcinoma and larger re-excisions are more likely to have residual cancer upon re-excision. Gender, age, and location of lesions are not predictive of positive re-excision. This information may add insight when evaluating a patient with positive margins and determining whether to proceed with re-excision.