Tumor Volume: An Adjunct Prognostic Factor in Cutaneous Melanoma
Measurement of tumor volume may be a helpful adjunct to established prognostic factors in cutaneous melanoma, including Breslow depth, presence or absence of ulceration, mitotic index, lymphovascular invasion, and microsatellites. This report expands on the theory that a tumor volume cutoff point of 250 mm3 as measured by surface area of the lesion (ie, longest vertical and horizontal measurements either based on clinical or gross pathological assessment) multiplied by the Breslow depth could serve as a potentially relevant predictor of sentinel lymph node (SLN) metastasis in both thin and thick invasive cutaneous melanomas, which prompted investigation of a larger sample size using the pathology database at our institution.
Practice Points
- Measurement of melanoma tumor volume using clinical area (length • width of the lesion before diagnostic biopsy) multiplied by Breslow depth may provide additional prognostic information.
- Further study is needed to validate the use of tumor volume as an adjunct to established histopathologic prognostic factors in cutaneous melanoma.
Comment
Decades after the concept of measuring tumor thickness in cutaneous melanomas was proposed by Dr. Alexander Breslow, it remains the most reliable predictor of prognosis in melanoma patients.2 Our study demonstrated that tumor volume may be contributory to thickness, despite our relatively imprecise assessment of tumor volume based on clinical or pathological reporting of primary tumor area. Because more than 90% of our tumor volume measurements were based on clinician reports of the lesion size before diagnostic biopsy rather than gross measurement of the tumor by the pathologist after biopsy, we believe that measurement and assessment of tumor volume could be readily incorporated into the clinical practice setting. Although we could not demonstrate a correlation between SLN positivity and tumor volume in T1 melanomas because none of the T1 tumors exhibited microscopic nodal metastasis, assessment of tumor volume may assist the clinician in patient management, using a 250-mm3 cutoff point. Gross tumor measurement is important to allow for accurate assessment of volume and would preferably be recorded by the clinician prior to biopsy with notation of clinical lesion size on the pathology requisition form, as is recommended in the American Academy of Dermatology’s melanoma practice guidelines.8
A prior assessment of 123 patients with invasive primary melanomas demonstrated that greater tumor volume (>250 mm3) was associated with metastasis across all tumor thicknesses.4 In T1 melanoma, no patients with a tumor volume less than 250 mm3 demonstrated SLN metastasis,4 suggesting that volume assessment may aid in consideration of staging with SLN biopsy in conjunction with tumor thickness and other established prognostic factors for SLN positivity in thin melanomas (eg, high mitotic index [particularly in tumors >0.75-mm thick]), histologic ulceration, and/or lymphovascular invasion).2,8
It should be noted, however, that lentigo maligna melanoma, which often is predominantly in situ with only focal papillary dermal invasion, may have an erroneously high tumor volume due to its larger total surface area. However, tumor volume would not be expected to correlate with tumor metastasis given the thin invasive component. The current study was limited by not accounting for melanoma subtype in the overall analysis.
A practical estimation of tumor volume based on clinical measurement of tumor size (ie, surface area of the suspicious lesion prior to biopsy) in combination with the pathologist’s assessment of Breslow depth may be a helpful adjunct to predicting likelihood of development of metastasis. We suggest that the concept of tumor volume should be subjected to more rigorous investigation with standardized clinical/prebiopsy measurement of the lesion; correlation with known histologic prognostic factors, SLN positivity, and/or development of additional nodal or visceral metastasis; and most importantly long-term patient outcome in terms of survival. Our preliminary data suggest the value of this enterprise.
