A total of 71 lesions in 64 consecutive patients, selected for surgical excision with frozen-section-assisted assessment of resection margins, were accrued. The distance of microscopic tumor extension beyond a gross lesion varied from 1 mm to 15 mm, with a mean of 5.2 mm. A margin of 10 mm was required to provide a 95% chance of obtaining clear resection margins. The microscopic tumor extent was positively correlated with the size of gross lesion, but not with other variables.

When RT is chosen as the therapeutic modality for nonmelanoma skin cancers, the determination of the area to be treated usually relies on visual delineation of the gross tumor and the inclusion of a margin of normal-appearing skin to account for microscopic tumor extent. The tissue volume that contains the subclinical microscopic tumor extent in addition to the gross tumor is equivalent to clinical target volume in the radiotherapy setting. Inadequate margin is associated with an increased risk of treatment failure, while excessive margin poses increased radiation morbidity. Therefore, a guideline for the margin of normal skin to be included within the RT volume would be very useful in clinical practice.

In the RT setting, little information exists with regard to how much margin should be given beyond a gross tumor volume for the treatment of BCC or SCC of the skin. A limited number of surgical series evaluating the extent of excision required to obtain clear resection margin have provided some insight into this matter. Determination of RT treatment volume remains very much subjective, however, and is usually based on a physician’s clinical judgment. That is, to some extent, due to the nature of radiation oncology practice, in which a significant proportion of cases referred for consideration of RT are often more complex, such as a large, ill-defined, lesion or recurrence after initial surgical excision.

Wolf  reported in a prospective study on 117 cases of previously untreated, well-demarcated BCC that a minimum margin of 4 mm was necessary to totally eradicate the tumor in more than 95% of cases. In this study, Mohs micrographic surgery was used for assessment of microscopic extent of tumor beyond gross tumor. It is important to note that this study targeted only those lesions with clinically well delineated tumor borders and no previous treatment. In a similarly designed prospective study for SCC, Brodland reported that 4-mm margins were adequate for most SCC, while a minimum of 6-mm margins were recommended for high-risk tumors (such as a size >2 cm, high histologic grade, and invasion of subcutaneous tissue).

In our series, nonmelanoma skin cancers have, on average, microscopic extension of 5.2 mm beyond the clinically visible tumor extent. However, extension could be as much as 15 mm. This magnitude was greater than those of the two surgical series described above. The primary reason for this variation lies most likely in the difference of case selection between the series. Our study, unlike the others, specifically targeted those tumors with poorly defined clinical borders, diameters >2 cm, or histopathologic features showing morpheaform or sclerotic patterns, and recurrence after previous treatment. In our series, 43.7%, 53.5%, and 52.1% were recurrent cancer, sclerosing type, and tumor >2 cm, respectively. These clinical and histologic features imply a higher likelihood of ill-defined tumor borders and thus an increased risk of underestimation of tumor extent. This speculation was further supported in that 70.4% of the lesions required more than one excision to obtain clear resection margins in our cohort. Another source of variation stems from potential imprecision in the way the distance of microscopic tumor extent beyond gross tumor was measured in our study. For example, if the plastic surgeon removed normal surrounding tissue more generously than would have been required, the margin of normal tissue required to obtain clear resection margins would be overestimated in our study.

Our study is consistent with the observation of other studies in that larger lesions have greater subclinical tumor extension. This observation must be taken into account in treatment planning. Other variables such as histology, the number of surgical attempts required to obtain clear margins, and the presence or absence of previous treatment did not show statistically significant correlation with the microscopic tumor extent in our cohort, although there was a trend toward positive correlation. This finding may be in part due to a small sample size of our study, resulting in insufficient power to detect such correla
 

Surgical margins for basal cell carcinoma. Wolf.  Arch Dermatol 1987; 123:340-4.

Basal cell carcinomas frequently extend beyond their visible borders. Therefore, the goal of surgical therapy must be to eradicate both the clinically apparent tumor and its microscopic extension into the surrounding normal-appearing skin. This entails excising the tumor along with a margin of clinically normal skin. Unfortunately, there is no agreement as to the optimal width of surgical margins. We therefore studied 117 cases of previously untreated, well-demarcated basal cell carcinoma. Prior to excision, the normal-appearing skin surrounding the tumor was marked in 2-mm increments. The tumor was then excised using Mohs micrographic surgery. The extent of the subclinical tumor invasion was calculated from the presurgical skin markings. For tumors with a diameter less than 2 cm, a minimum margin of 4 mm was necessary to totally eradicate the tumor in more than 95% of cases.

Surgical margins for excision of primary cutaneous squamous cell carcinoma. Brodland. J Am Acad Dermatol 1992; 27:241-8.

No guidelines for the margin of resection of cutaneous squamous cell carcinoma have been based on data measuring subclinical tumor extension, as have been formulated for basal cell carcinoma. Guidelines for appropriate margins of excision of primary cutaneous squamous cell carcinoma were formulated on the basis of a prospective study of subclinical microscopic tumor extension. RESULTS: Four millimeter margins were adequate for most squamous cell carcinomas. However, certain tumor characteristics were associated with a greater risk of subclinical tumor extension and included size of 2 cm or larger, histologic grade 2 or higher, invasion of the subcutaneous tissue, and location in high-risk areas. CONCLUSION: Minimal margins of excision of 4 mm around the clinical borders of the squamous cell carcinoma are proposed for all but the high-risk tumors, in which at least a 6 mm margin is recommended.

Do plastic surgeons resect basal cell carcinomas too widely? A prospective study comparing surgical and histological margins    Bisson MA, Br J Plast Surg. 2002;55:293–297

Basal cell carcinoma is a common condition facing the plastic surgeon. When formally excised, a surrounding margin of normal skin is included in an attempt to ensure complete excision. We set out to investigate our excision margins in a prospective study of 100 basal cell carcinomas in 86 patients treated by conventional surgical excision. Given a 3 mm margin, 96% of lesions would have been excised completely.

Excision margins for nonmelanotic skin cancer.  Thomas. Plast Reconstr Surg. 2003 Jul;112(1):57-63.

Scientific evidence for advisable excision margins for nonmelanotic skin carcinoma is poorly documented. Recommended excision margins vary from 2 to 15 mm. A prospective study was performed on 150 skin lesions excised.U Diagnostic accuracy was 81 percent for basal cell an 59 percent for squamous cell carcinoma. The average diameter of the basal cell carcinoma was 12.1 mm; 47 percent of these lesions had a diameter of less than 10 mm. The average diameter of the squamous cell carcinoma was 16.9 mm; 26 percent of these lesions had a diameter of less than 10 mm. The mean surgical margin was 4.2 mm (3.2 mm adjusted for shrinkage), whereas the mean microscopic lateral margin was 3.4 mm. Overall, complete excision was achieved for 98 percent of basal cell carcinoma and 100 percent of squamous cell carcinoma. The raw data were analyzed to assess the suitability of 1-, 2-, 3-, or 4-mm surgical excision margins. A 4-mm surgical margin would give a microscopic lateral margin beyond one microscopic high-power field (0.5 mm) in 96 percent of cases of basal cell carcinoma and in 97 percent of cases of squamous cell carcinoma. The authors recommend a 4-mm surgical margin as the optimal treatment for skin lesions clinically diagnosed as basal cell or squamous cell carcinoma that are suitable for excision in an outpatient facility. Well-demarcated lesions, such as a nodular basal cell carcinoma, may be excised with a 3-mm margin.