Challenges in sentinel node pathology in the era of adjuvant treatment

The difficulty with measuring the largest melanoma tumour diameter in sentinel lymph nodes

Identification of sentinel node (SN) metastases can set the adjuvant systemic therapy indication for stage III melanoma patients. For stage IIIA patients, a 1.0 mm threshold for the largest SN tumour diameter is used. Therefore, uniform reproducible measurement of its size is crucial. At present, the number of deposits or their microanatomical sites are not part of the inclusion criteria for adjuvant treatment. The goal of the current study was to show examples of the difficulty of measuring SN melanoma tumour diameter and teach how it should be measured. Histopathological slides of SN-positive melanoma patients were retrieved using the Dutch Pathology Registry (PALGA). Fourteen samples with the largest SN metastasis around 1.0 mm were uploaded via tele-pathology and digitally measured by 12 pathologists to reflect current practice of measurements in challenging cases. Recommendations as educational examples were provided. Microanatomical location of melanoma metastases was 1 subcapsular, 2 parenchymal and 11 combined. The smallest and largest difference in measurements were 0.24 mm and 4.81 mm, respectively. 11/14 cases (78.6%) showed no agreement regarding the 1.0 mm cut-off. The median discrepancy for cases ≤5 deposits was 0.5 mm (range 0.24-0.60, n=3) and 2.51 mm (range 0.71-4.81, n=11) for cases with ≥6 deposits. Disconcordance in measuring SN tumour burden is correlated with the number of deposits. Awareness of this discordance in challenging cases, for example, cases with multiple small deposits, is important for clinical management. Illustrating cases to reduce differences in size measurement are provided.

The Association of Guideline-Concordant Sentinel Lymph Node Biopsy for Melanoma at Minority-Serving Hospitals

BACKGROUND

Minority-serving hospitals (MSHs) have been associated with lower guideline adherence and worse outcomes for various cancers. However, the relationship among MSH status, concordance with sentinel lymph node biopsy (SLNB) guidelines, and overall survival (OS) for patients with cutaneous melanoma is not well studied.

METHODS

The National Cancer Database was queried for patients diagnosed with T1a*, T2, and T3 melanoma between 2012 and 2017. MSHs were defined as the top decile of institutions ranked by the proportion of minorities treated for melanoma. Based on National Comprehensive Cancer Network guidelines, guideline-concordant care (GCC) was defined as not undergoing SLNB if thickness was < 0.76 mm without ulceration, mitosis ≥ 1/mm², or lymphovascular invasion (T1a*), and performing SLNB for patients with intermediate thickness melanomas between 1.0 and 4.0 mm (T2/T3). Multivariable logistic regressions examined associations with GCC. The Kaplan-Meier method and log-rank tests were used to evaluate OS between MSH and non-MSH facilities.

RESULTS

Overall, 5.9% (N = 2182/36,934) of the overall cohort and 37.8% of minorities (n = 199/527) were managed at MSHs. GCC rates were 89.5% (n = 33,065/36,934) in the overall cohort and 85.4% (n = 450/527) in the minority subgroup. Patients in the overall cohort (odds ratio [OR] 0.85; p = 0.02) and the minority subgroup (OR 0.55; p = 0.02) were less likely to obtain GCC if they received their care at MSHs compared with non-MSHs. Minority patients receiving care at MSHs had a decreased survival compared with those treated at non-MSHs (p = 0.002).

CONCLUSIONS

Adherence to SLNB guidelines for melanoma was lower at MSHs. Continued focus is needed on equity in melanoma care for minority patients in the United States.

High discordance rate in assessing sentinel node positivity in cutaneous melanoma: Expert review may reduce unjustified adjuvant treatment

INTRODUCTION

Identification of sentinel node (SN) metastases can set the adjuvant systemic therapy indication for patients with stage III melanoma. Studies re-evaluating the diagnosis of initially positive SN biopsies are scarce.

MATERIALS AND METHODS

Dutch patients with melanoma who underwent SN biopsy between 2003 and 2014 were selected from PALGA, the Dutch Pathology Registry. Histopathological slides of SN-positive patients were retrieved for review. A random sample was reassessed by an expert melanoma pathologist. Recurrence-free survival (RFS) of patients who were misclassified (false-positive) was compared with those with a true positive SN status. For comparison, a group of SN-negative patients was included. Multivariable logistic analysis was performed to assess clinicopathological characteristics associated with misclassification of SN status.

RESULTS

Diagnosis was downgraded from melanoma metastasis to nodal nevus in 38 of the 322 reviewed patients (11.8%). Considering the inclusion criteria of phase III adjuvant trials, at least 4.3% of patients would have falsely qualified for adjuvant therapy. In multivariable analysis, patients with a low SN tumour burden and subcapsular SN tumour location had a significantly higher chance of being misclassified. The five-year RFS of the 38 downgraded patients was 86.7% (95% confidence interval [CI] = 72.6-96.6), similar to the 85.9% (95% CI = 84.9-86.8, p = 0.18) for 6413 SN-negative patients and better than the 53.2% (95% CI = 47.2-59.9, p = 0.009) of 284 patients who were truly SN positive upon review.

CONCLUSION

More than 10% of originally positive SN biopsies of patients with melanoma concern misclassified nodal nevi. We advocate that when adjuvant treatment is considered in patients with stage III melanoma, SN biopsies should be reassessed by an expert melanoma pathologist.