The use of SLNB for thick cutaneous melanomas has nevertheless remained controversial due to the nihilistic belief that thick melanomas are associated with an unacceptably high likelihood of distant metastatic disease [14]. Given that only half of all patients with thick primary melanomas will be alive 10 years after their diagnosis, [2] some physicians believe that such patients are unlikely to benefit from SLNB because their outcome will be dictated by their occult metastasis and not the presence or absence of sentinel lymph node metastasis.

We excluded patients with mucosal melanoma, those without a biopsy-proven diagnosis, those diagnosed at autopsy, patients whose lymph node evaluation was unknown, or other than SLNB “yes” or SLNB “no”. Patients who had a lymph node evaluation other than SLNB were also excluded, as it was assumed that these patients likely had clinically evident, palpable disease and underwent formal complete lymphadenectomy.

To assess the proportion of patients with thick primary melanomas undergoing SLNB over time, we tabulated the number of SLNB procedures performed relative to the total number of cases of thick primary cutaneous melanoma per year.

Patient and tumor characteristics of the study population according to whether or not a SLNB was performed are included in Table 1. When divided into those that received a SLNB and those that did not receive a SLNB, the two groups were found to significantly differ with respect to patient age, mean Breslow tumor depth, and tumor location. Those in the no SLNB group had a greater proportion of elderly patients (80 years or older), thinner melanomas, and a greater proportion of head/neck tumor sites than those in the SLNB group.

In our current study of 1,981 patients with thick primary cutaneous melanoma, 41.8% did not have a SLNB. This is higher than the 19.5% underuse rate reported by Meguerditchian et al. Most in an institutional review of 113 similar patients [16]. There are several possible explanations for this discrepancy. Among them is an important limitation of the SEER database. SEER does not provide information on individual patient comorbidities that may influence the recommendation to perform a SLNB. For example, a surgeon may be more likely to perform a SLNB on a healthy 80-year-old man than a similarly aged man with diabetes, congestive heart failure, and exercise limiting chronic obstructive pulmonary disease, but SEER cannot shed light on this aspect of the treatment decision-making process.

We found that the likelihood of receiving a SLNB was inversely proportional with age, with patients aged 60 years and older having a decreased likelihood of undergoing a SLNB. This finding is consistent with our previously reported finding that elderly patients are less likely to receive SLNB for intermediate thickness melanoma [17]. Older patients are more likely than their younger counterparts to have comorbidities that may influence the decision of whether or not to offer SLNB. Significant comorbidities, when added to the risk of distant metastasis and subsequent mortality from a thick primary cutaneous melanoma, may be perceived to overshadow any potential benefit obtained from the SLNB in terms of accurate staging and early complete lymphadenectomy in the case of node positive disease. Poorer overall survival among elderly patients is to be expected. However, Göpper et al. found that, eventhough increasing age was associated with decreased overall survival, this effect was dominated by the prognostic importance of the sentinel lymph node status [18]. Among the largest single institution series was reported by Gajdos et al. [19]. They examined 227 patients with thick (T4) melanoma who underwent SLNB from 1997 to 2007 and similarly found that increasing age negatively influenced overall survival. Again, however, the influence of advancing age was dominated by the status of the sentinel lymph node. When patients were further categorized into sentinel lymph node negative and sentinel lymph node positive groups, increasing age was found to be a prognostic factor only for the sentinel lymph node negative group. Together, these findings indicate that, even as age increases, the sentinel node status may still provide valuable prognostic information.

In our study, we noted that patients of unknown race/ethnicity were significantly less likely to undergo SLNB. We have no definitive explanation for this finding. Our patient population was > 90% white, with very few (N = 16) being of unknown race/ethnicity. It is most likely that this finding is unreliable for this reason.

Increasing Breslow thickness negatively influenced the likelihood of receiving a SLNB in our study. Our multivariate model assessed the likelihood of receiving a SLNB for each 0.01mm increase in Breslow thickness. For every 0.01mm increase in Breslow depth, there was a 0.5% decrease in the odds of receiving a SLNB. This translates into a 14.5% decrease in the odds of receiving a SLNB for every 1mm increase in Breslow thickness. This is likely explained by a growing sense of nihilism about the likelihood of occult distant metastatic disease as the primary tumor increases in thickness. It is somewhat unclear if the nihilism is warranted, however. Carlson et al. studied 114 patients with thick melanoma who underwent SLNB and found that the thickest tumors (>6mm) were not associated with increased risks of overall or relapse-free survival [20]. Using tumor thickness as a continuous variable in a multivariate model, Gutzmer et al. failed to identify any influence of increasing melanoma thickness on overall survival [6]. Similarly, Gershenwald et al. noted no influence of increasing tumor thickness on either disease-free or overall survival among 131 patients with thick melanomas undergoing SLNB [5]. Both Ferrone et al. [4] and Jacobs et al. [7] documented a higher risk of disease recurrence with increasing tumor thickness, but they did not examine any influence on overall survival.

We found that patients with thick desmoplastic melanomas were less likely to undergo SLNB. It is possible that SLNB was less commonly offered in these patients because desmoplastic melanomas have been shown to have lower rates of sentinel lymph node metastasis [21]. Additionally, desmoplastic melanomas are more common on the head/neck, and these areas may be more challenging for lymphatic mapping and SLNB may therefore be deferred in favor of clinical observation. Indeed, in our analysis, relative to head/neck primary sites, patients with melanomas of the trunk and extremities were approximately twice as likely to undergo SLNB.

Although the presence of tumor ulceration plays a significant role in several models assessing the prognostic utility of SLNB in patients with thick melanoma, [4, 5, 7, 20] ulceration did not seem to influence the use of SLNB in our patient cohort. This could reflect a relationship between tumor ulceration and Breslow thickness. As previously stated, we found that increasingly thick melanomas were less likely to undergo SLNB. Due to tumor ulceration, the depth of some melanomas may be underestimated. With these “thinner” melanomas being perceived as “less risky” for occult metastasis, surgeons may opt to pursue SLNB more readily. However, Bilimoria et al. examined the records of 8,525 stage IB and II melanoma patients in the National Cancer Data Base and found that those with no tumor ulceration were less likely to undergo SLNB [22].

Our data may be subject to selection bias, since we only included patients for whom data was complete regarding whether or not SLNB was performed. Such a decision provided us with a more homogeneous population and allowed us to exclude patients that underwent a complete lymphadenectomy, likely because of clinically palpable nodal disease. Nevertheless, we may have excluded patients that would have otherwise altered our measured outcomes. Finally, SEER does not provide information on patient-level socioeconomic status such as monthly/yearly income or surrogates of socioeconomic status like education level or insurance status. Such factors may influence access to optimal cancer care and may partially explain the relatively high percentage of patients not undergoing SLNB in our study.