T1b Melanomas Research Articles

Impact of an Online Risk Calculator for Sentinel Node Positivity on Management of Patients with T1 and T2 Melanomas

BackgroundPredicting which patients with American Joint Committee on Cancer (AJCC) T1–T2 melanomas will have a positive sentinel lymph node (SLN) is challenging. Melanoma Institute Australia (MIA) developed an internationally validated SLN metastatic risk calculator. This study evaluated the nomogram’s impact on T1–T2 melanoma patient management at MIA.MethodsSLN biopsy (SLNB) rates were compared for the pre- and post-nomogram periods of 1 July 2018–30 June 2019 and 1 August 2020–31 July 2021, respectively.ResultsOverall, 850 patients were identified (pre-nomogram, 383; post-nomogram, 467). SLNB was performed in 29.0% of patients in the pre-nomogram group and 34.5% in the post-nomogram group (p = 0.091). The overall positivity rate was 16.2% in the pre-nomogram group and 14.9% in the post-nomogram group (p = 0.223). SLNB was performed less frequently in T1a melanoma patients in the pre-nomogram group (1.1%, n = 2/177) than in the post-nomogram group (8.6%, n = 17/198) [p ≤ 0.001]. This increase was particularly for melanomas with a risk score ≥ 5%, with an SLN positivity rate of 11.8% in the post-nomogram group (p = 0.004) compared with zero. For T1b melanomas with a risk score of > 10%, the SLNB rate was 40.0% (8/20) pre-nomogram and 75.0% (12/16) post-nomogram (p = 0.049).ConclusionsIn this specialized center, the SLN risk calculator appears to influence practice for melanomas previously considered low risk for metastasis, with increased use of SLNB for T1a and higher-risk T1b melanomas. Further evaluation is required across broader practice settings. Melanoma management guidelines could be updated to incorporate the availability of nomograms to better select patients for SLNB than previous criteria.

Influence of Anatomic Locations of T1b Melanomas and Patient Age on Outcomes.

There are no guidelines on when to more strongly recommend sentinel lymph node biopsy (SLNB) for T1b melanomas. To examine whether anatomic locations of T1b melanomas and patient age influence metastases. We conducted a retrospective study using data from two hospitals in Los Angeles County from January 2010 through January 2020. Out of 620 patients with primary melanomas, 566 melanomas were staged based on the American Joint Committee on Cancer 8th edition melanoma staging. Forty-one were T1b, of which 13 were located on the face/ear/scalp and 28 were located elsewhere. T1b melanomas located on the face/ear/scalp had an increased risk of lymph node or distant metastasis compared with other anatomic sites (31% vs 3.6%, P=0.028). For all melanomas, the risk of lymph node or distant metastasis decreased with age of 64 years or greater (P<0.001 and P=0.034). For T1b melanomas, the risk of distant metastasis increased with increasing age (P=0.047). Data were from a single county.  Conclusion: T1b melanomas of the face/ear/scalp demonstrated a higher risk of lymph node or distant metastasis and may help guide the recommendation of SLNB, imaging, and surveillance. Younger patients may be more strongly considered for SLNB and older patients with T1b melanomas may warrant imaging.  J Drugs Dermatol. 2024;23(5):306-310. doi:10.36849/JDD.7667.

Cost evaluation of the Merlin assay for predicting melanoma sentinel lymph node biopsy metastasis.

The Merlin assay for melanoma-risk assessment has become commercially available to reduce the rate of unnecessary sentinel lymph node biopsies (SLNB) in SLNB-eligible patients with cutaneous melanoma. Merlin low-risk patients are recommended to undergo wide local excision (WLE) of the primary tumor, whereas Merlin high-risk patients are recommended to undergo both SLNB and WLE. Here, we compared the cost of a Merlin testing strategy to that of a no-testing strategy (usual care) before prescribing SLNB. We identified T1 and T2 patients who underwent WLE and SLNB but not completion lymph node dissection between 2007 and 2018. Controls were T1 patients who only underwent WLE. Costs for WLE and SLNB were calculated by converting institutional cost data to standardized Medicare reimbursement rates. We then developed a decision tree to compare the cost of Merlin testing to that of a no-testing strategy (usual care). The average standardized cost of WLE was $2066, whereas the cost of WLE and SLNB was $11,976 based on Medicare rates. At a cost below $7350 for T1b melanoma and $4600 for T1b to T2 melanoma, Merlin testing was cost-saving compared to a no-testing strategy (usual care), assuming Medicare reimbursement rates. Merlin testing for T1b and T2 melanoma is potentially cost saving depending on the cost of the molecular assay and SLNB reimbursement rates. In addition to being cost saving, Merlin is expected to improve health-related quality of life.

Differences in sentinel lymph node biopsy utilization in eligible melanoma patients treated with Mohs micrographic surgery or wide local excision: A population-based logistic regression model and survival analysis

Primary melanoma management relies on tumor extirpation and staging sentinel lymph node biopsy (SLNB) in eligible patients. This study compares SLNB utilization in patients undergoing wide local excision (WLE) or Mohs micrographic surgery (MMS). American Joint Committee on Cancer seventh edition≥patients with T1b melanoma undergoing WLE or MMS in the Surveillance, Epidemiology, and End Results program were included. Propensity score matching was performed to compare patients who underwent MMS or WLE. Kaplan-Meier analysis and Fine-Gray cumulative incidence functions were used for overall and melanoma-specific survival. Eight hundred twenty-five MMS cases and 38,760 WLE cases were identified. SLNB was performed in 32.61% of MMS patients and 61.77% of WLE patients with positive rates of 12.5% and 14.82%, respectively. Multiple logistic regression of factors associated with SLNB utilization revealed that WLE, male gender, younger age, extremity location, and nodular and rare melanoma subtypes were significantly associated with increased odds of receiving SLNB whereas head and neck location and lentigo maligna melanoma subtype were significantly less likely to receive SLNB. Potential selection bias from a retrospective data set. Patients receiving WLE for≥T1b melanoma are more likely to receive a SLNB than patients undergoing MMS.

The importance of mitosis ≥2 in selecting patients with T1 cutaneous melanomas for sentinel lymph node biopsy.

The 8th Edition of the American Joint Committee on Cancer (AJCC) Staging Manual removed the mitotic rate (MR) as a staging criterion for T1 melanomas, thus leading to a debate on sentinel lymph node biopsy (SLNB) in thin melanomas. This study investigates whether MR plays a role in selecting patients with T1 melanoma for SLNB. We analyzed clinical and histological data from the Florence Melanoma & Skin Cancer Unit database for 313 patients with a single thin melanoma who had undergone SLNB. We determined sentinel lymph node (SLN) positivity percentages in T1 melanomas according to the AJCC 8th Edition focusing on MR. Of the 313 T1 patients, 108 had MR = 0, 127 had MR = 1 and 78 had MR ≥2. The overall SLN positivity rate was 8.6%, (5.6% with MR = 0, 6.3% with MR = 1 and 16.7% with MR ≥2). The SLNB positivity rate in T1b melanomas was 12.1%, (8.5% with MR = 0, 5.7% with MR = 1 and 24.4% with MR ≥2), whereas in T1a melanomas it was 5.8%, (3.3% with MR = 0, 6.8% with MR = 1 and 8.1% with MR ≥2). In a logistic regression analysis, MR ≥2 had an odds ratio of almost three in comparison with MR = 0/1 also adjusting for thickness. Thus, MR ≥2 significantly predicted SLN metastases in T1 melanomas. Of those patients with positive SLN, 37% were classified as T1a according to the AJCC 8th edition. These findings underline the importance of MR ≥2 in selecting patients with T1 cutaneous melanomas for SLNB.

32579 Influence of anatomic locations of T1b melanomas and patient age on outcomes

Background: T1b melanomas warrant discussion and consideration of sentinel lymph node biopsy. There are no current recommendations to help guide the clinician regarding when to more strongly recommend sentinel lymph node (SLN) biopsy for T1b melanomas.

ASO Visual Abstract: Use and Costs of Sentinel Lymph Node Biopsy in Nonulcerated T1b Melanoma: Analysis of a Population-Based Registry

ASO Visual Abstract: Use and Costs of Sentinel Lymph Node Biopsy in Nonulcerated T1b Melanoma: Analysis of a Population-Based Registry

Validation of CP‐GEP (Merlin Assay) for predicting sentinel lymph node metastasis in primary cutaneous melanoma patients: A U.S. cohort study

BackgroundApproximately 85% of melanoma patients who undergo a sentinel lymph node biopsy (SLNB) are node‐negative. Melanoma incidence is highest in patients ≥65 years, but their SLNB positivity rate is lower than in younger patients. CP‐GEP, a model combining clinicopathologic and gene expression variables, identifies primary cutaneous melanoma (CM) patients who may safely forgo SLNB due to their low risk for nodal metastasis. Here, we validate CP‐GEP in a U.S. melanoma patient cohort.MethodsA cohort of 208 adult patients with primary CM from the Mayo Clinic and West Virginia University was used. Patients were stratified according to their risk for nodal metastasis: CP‐GEP High Risk and CP‐GEP Low Risk. The main performance measures were SLNB reduction rate (RR) and negative predictive value (NPV).ResultsSLNB positivity rate for the entire cohort was 21%. Most patients had a T1b (34%) or T2a (31%) melanoma. In the T1‐T2 group (153 patients), CP‐GEP achieved an SLNB RR of 41.8% (95% CI: 33.9‐50.1) at an NPV of 93.8% (95% CI: 84.8‐98.3). Subgroup analysis showed similar performance in T1‐T2 patients ≥65 years of age (51 patients; SLNB positivity rate, 9.8%): SLNB RR of 43.1% (95% CI: 29.3‐57.8) at an NPV of 95.5% (95% CI: 77.2‐99.9).ConclusionWe confirmed the potential of CP‐GEP to reduce negative SLNB in all relevant age groups. Our findings are especially relevant to patients ≥65 years, where surgery is often elective. CP‐GEP may guide SLNB decision‐making in clinical practice.

Use and Costs of Sentinel Lymph Node Biopsy in Non-Ulcerated T1b Melanoma: Analysis of a Population-Based Registry.

The utility of sentinel lymph node biopsy (SLNB) for non-ulcerated T1b melanoma is debated and associated costs are poorly characterized. Prior work using institutional registries may overestimate the incidence of nodal positivity in this population. The aim of this study was to estimate the use of SLNB, positivity prevalence, and procedural costs in patients with non-ulcerated T1b melanoma using a population-based registry. We identified patients with clinically node-negative, non-ulcerated melanoma 0.8-1.0mm thick (T1b according to the 8th edition standard of the American Joint Committee on Cancer) in the Surveillance, Epidemiology, and End Results database from 2010 to 2016. The prevalence of SLNB procedures and positive sentinel nodes were calculated. Factors associated with SLNB and sentinel node positivity were assessed using logistic regression. Medicare reimbursement costs and patient out-of-pocket expenses for SLNB and wide local excision (WLE) versus WLE alone were estimated. Among 7245 included patients, 3835(53%) underwent SLNB, 156 (4.1%, 95% confidence interval 3.5-4.7) of whom had a positive SLNB. Younger age, >1 mitosis per mm2, female sex, and truncal tumor location were associated with higher odds of positivity. The estimated SLNB cost to identify one patient with stage III disease was $71,700 (range $54,648-$83,172). Out-of-pocket expenses for a Medicare patient were estimated to be $652 for a WLEandSLNB and $79 for a WLE alone. In this population-based study, only 4% of selected non-ulcerated T1b patients had a positive SLNB, which is lower than prior reports. At the population level, SLNB is associated with high costs per prognostic information gained.

Five-year survival in patients with nodular and superficial spreading melanomas in the US population

Although superficial spreading melanomas (SSM) are diagnosed as thinner lesions, nodular melanomas (NM) have a more rapid growth rate and are biologically more aggressive compared with other histologic subtypes. To determine the difference in 5-year relative survival in patients with NM and SSM at the same Breslow depth and TNM stage. A population-based cross-sectional analysis compared the 5-year relative survival of patients with NM and SSM using data from the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER)∗Stat software (version 8.2.1-8.3.5). Chi-square tests compared the proportions, and Kaplan-Meier method with Z-score compared 5-year relative survival. For patients receiving a diagnosis between 2004 and 2009, 5-year relative survival was lower in NM compared with SSM (53.7% vs 87.3%; Z score, -41.35; P<.001). Similarly, for patients receiving a diagnosis between 2010 and 2015, 5-year relative survival was lower in NM compared with SSM (61.5% vs 89.7%; Z score, -2.7078; P<.01). Subgroup analyses showed inferior survival in NM in T1b, and survival differences remained significant after excluding patients with nodal or distant metastases. Five-year relative survival is worse in NM compared with SSM especially in T1b, T2a, and T2b melanomas. Melanoma subtype should be taken into consideration when making treatment recommendations.

Sentinel Node Biopsy in Non-Ulcerated T1b Melanoma: Analysis of Incidence and Cost Using a Population-Based Registry

Herb, Joshua MD; Stitzenberg, Karyn B. MD, FACS; Meyers, Michael O. MD, FACS Author Information

ASO Author Reflections: Role of Sentinel Lymph Node Biopsy in T1b Melanoma.

ASO Author Reflections: Role of Sentinel Lymph Node Biopsy in T1b Melanoma.

Sentinel Lymph Node Biopsy for T1b Melanoma: Balancing Prognostic Value and Cost.

The purpose of this study is to report the additional prognostic information and cost associated with sentinel lymph node biopsy (SLNB) for patients with T1b melanoma. An institutional database was queried for patients with T1b melanoma (0.8-1.0mm or < 0.8mm with ulceration) with at least 5years of follow-up. Results of SLNB, completion lymphadenectomy (CLND), recurrence, and melanoma-specific survival (MSS) were assessed. Institutional costs of melanoma care were converted to Medicare proportional dollars. A Markov model was created to estimate long-term costs. Among the total 392 patients, 238 underwent SLNB. Median follow-up was 10.5years. SLNB was positive in 19 patients (8.0%). Patients who underwent SLNB had higher 10-year nodal recurrence-free survival (98.6% vs. 91.2%, p < 0.001) but not MSS (94.4% vs. 93.2%, p = 0.55). Ulceration (HR 4.7, p = 0.022) and positive sentinel node (HR 11.5, p < 0.001) were associated with worse MSS. Estimates for 5-year costs reflect a fourfold increase in total costs of care associated with SLNB. However, a treatment plan that forgoes adjuvant therapy for resected stage IIIA melanoma but offers systemic therapy for a node-basin recurrence would nullify the additional cost of SLNB. SLNB is prognostic for T1b melanoma. Its impact on the overall cost of melanoma care is intimately tied to systemic therapy in the adjuvant and recurrent settings.

Regional nodal metastasis and 5-year survival in patients with thin melanoma in Queensland: a population-based study.

Optimal management of regional lymph nodes for thin cutaneous melanoma is uncertain. We evaluated regional lymph node involvement and 5-year melanoma-specific survival (MSS) in patients with thin (≤1 mm) primary melanoma. Patients with a melanoma, American Joint Committee on Cancer Staging 8th Edition pT1a (<0.8 mm) or pT1b (ulceration; and/or 0.8-1.0 mm), diagnosed during 2001-2015 were identified from the Queensland Oncology Repository. We extracted demographic, pathology and clinical details, including sentinel lymph node biopsy (SLNB), regional nodal dissection and nodal recurrence. Poisson regression was used to assess recurrence risk in patients who did not undergo SLNB. The 5-year MSS was calculated using the Kaplan-Maier method with Cox regression to compare survival outcomes according to SLNB performance. Of the 27 824 eligible patients, 240 (0.9%) underwent SLNB. One hundred and seventy-eight patients (0.6%) without SLNB had nodal recurrence. Of the 4848 patients with a pT1b lesion, 166 (3.4%) had SLNB with 12 (7.2%) positive; of the remainder, 99 (2.1%) had clinical recurrence. Risk of recurrence was higher in males, nodular subtype and T1b lesions and lower if patients were aged >60 years. The 5-year MSS was similar for observed and SLNB cohorts (99.66% versus 98.92%) but worse for T1b lesions (98.90%) and clinical nodal recurrence (66.89%). Overall prognosis for T1 melanoma is excellent with nodal involvement being rare. However, the American Joint Committee on Cancer 8th Edition T1b melanoma correlates with significantly worse 5-year MSS and increased regional nodal recurrence (notably for 0.8-1.0 mm lesions with ulceration). Further characterization of high-risk groups for nodal positivity that impacts patient outcome is needed for the pT1 melanoma cohort.

Melanoma pathology reporting and staging.

The pathological diagnosis of melanoma can be challenging. The provision of an appropriate biopsy and pertinent history can assist in establishing an accurate diagnosis and reliable estimate of prognosis. In their reports, pathologists should document both the criteria on which the diagnosis was based as well as important prognostic parameters. For melanoma, such prognostic parameters include tumor thickness, ulceration, mitotic rate, lymphovascular invasion, neurotropism, and tumor-infiltrating lymphocytes. Disease staging is important for risk stratifying melanoma patients into prognostic groups and patient management recommendations are often stage based. The 8th edition American Joint Committee on Cancer (AJCC) Melanoma Staging System was implemented in 2018 and several important changes were made. Tumor thickness and ulceration remain the key T category criteria. T1b melanomas were redefined as either ulcerated melanomas <1.0 mm thick or nonulcerated melanomas 0.8-1.0 mm thick. Although mitotic rate was removed as a T category criterion in the 8th edition, it remains a very important prognostic factor and should continue to be documented in primary melanoma pathology reports. It was also recommended in the 8th edition that tumor thickness be recorded to the nearest 0.1 mm (rather than the nearest 0.01 mm). In the future, incorporation of additional prognostic parameters beyond those utilized in the current version of the staging system into (web based) prognostic models/clinical tools will likely facilitate more personalized prognostic estimates. Evaluation of molecular markers of prognosis is an active area of current research; however, additional data are needed before it would be appropriate to recommend use of such tests in routine clinical practice.

JAAD Game Changers: Variability in mitotic figures in serial sections of thin melanomas

Capsule Summary•A rigorous approach to accurately capture mitotic activity and expected density of mitoses in T1b melanomas is needed.•We describe the variability in mitoses between serial sections and the minimum number of sections to review (5 sequential sections).•This will increase accuracy and should help prevent under diagnosis.How did this article change the practice of dermatology?Looking back at this article in 2018, these authors were ahead of their time in demonstrating the difficulty in determining the mitotic rate in melanomas.1 The American Joint Committee on Cancer evaluated survival outcome of melanomas with <0.8-mm tumor thickness (Breslow) and determined that primary ulceration and tumor thickness were more important than mitotic rate in determining prognosis, and mitotic rate no longer is considered in staging of these tumors. T1a tumors are nonulcerated melanomas <0.8 mm in thickness, and T1b tumors are (1) 0.8 to 1.0 mm in thickness regardless of ulceration status or (2) ulcerated melanomas <0.8 mm in thickness.1

Early Melanoma Nodal Positivity and Biopsy Rates Before and After Implementation of the 7th Edition of the AJCC Cancer Staging Manual

There has been a continued increase in the incidence of newly diagnosed melanomas, most of which are T1 melanomas. The associations between changes in tumor staging, implemented with the 7th edition of the AJCC Cancer Staging Manual (AJCC 7), and sentinel lymph node biopsy rates and nodal positivity rates remain to be seen. To evaluate the change that the implementation of the AJCC 7 had on staging criteria and the distribution of thin melanomas requiring nodal surgery and nodal positivity rates. Retrospective cross-sectional study from 2004 through 2013 of all adults (≥18 years) diagnosed with a T1 (Breslow depth ≤1.0 mm) melanoma using The National Cancer Database that captures 70% of all newly diagnosed cancers from accredited Commission on Cancer organizations, including both academic and community settings. Data were analyzed in May 2017. Patients were grouped together based on year of diagnosis, before and after 2009. To determine the sentinel lymph node biopsy rate before and after the implementation of the AJCC 7. A total of 141 280 patients met inclusion criteria. Of 86 846 patients diagnosed from 2004 through 2009, 53.7% (49 644) were male and had a mean (SD) age of 57.7 (16.4) years. Of 54 434 patients diagnosed from 2010 through 2013, 54.3% (31 086) were male and had a mean (SD) age of 59.5 (15.9) years. After 2010, there was a 3.8% decrease in the number of nodal surgeries performed (32 485 of 86 846 patients [37.6%] vs 18 379 of 54 434 patients [33.8%]; P < .001). The nodal positivity rate decreased 1.0% from (9.8% [3166 of 86 846] to 8.8% [1618 of 54 434]) (P < .001). An increase in the proportion of T1b melanomas being evaluated, from 48.8% to 62.2%, was seen (P < .001). Of T1b melanomas that underwent nodal evaluation from 2004 through 2009, 74.0% had Clark level IV (invasion of the reticular dermis) or Clark level V (invasion of the deep, subcutaneous tissue) and 9.5% were ulcerated. From 2010 through 2013, of the T1b melanomas undergoing nodal evaluation, 82.6% had an elevated mitotic rate only, 3.7% were ulcerated, and 13.7% had both ulceration and an elevated mitotic rate. It appears that after the institution of AJCC 7, there was an overall decrease in the number of T1 melanomas undergoing nodal biopsy without a clinically relevant change in sentinel lymph node positivity, with an increase in the number of T1b melanomas undergoing nodal evaluation.

Should Sentinel Lymph Node Biopsy Be Performed for All T1b Melanomas in the New 8th Edition American Joint Committee on Cancer Staging System?

In the 8th edition of the American Joint Committee on Cancer melanoma staging system, the T1b category has been redefined based solely on thickness and ulceration. National Comprehensive Cancer Network guidelines recommend consideration of sentinel lymph node biopsy (SLNB) for all patients with T1b melanomas (0.8 to 1.0 mm thick). We hypothesized that the new staging system would lead to excessive use of SLNB in patients with non-ulcerated T1b melanomas with a low risk of positive sentinel lymph nodes. The National Cancer Database 2015 Melanoma Public Use File was used to select patients undergoing SLNB for thin T1 cutaneous melanoma from 2010 to 2015. Clinicopathologic risk factors for having a positive SLNB were evaluated. Univariable and multivariable logistic regression models and classification and regression tree analysis were performed to identify groups with high and low risk of positive SLNB. We selected patients undergoing SLNB without ulceration with thickness 0.75 to 1.04 mm, staged T1b in the new 8th edition American Joint Committee on Cancer by thickness criteria alone (6,894 patients). Independent risk factors for a positive sentinel lymph node were age 56 years or younger (odds ratio [OR] 1.74; 95% CI 1.38 to 2.17), thickness 1.0 vs 0.8 to 0.9 mm (OR 1.36; 95% CI 1.09 to 1.70), female sex (OR 1.36; 95% CI 1.09 to 1.69), and mitotic rate ≥1/mm2 (OR 2.01; 95% CI 1.54 to 2.64). Classification and regression tree analysis identified 2 groups based on age, mitotic rate, and thickness with a risk of positive SLNB <5%. These 2 groups made up 55% of T1b, nonulcerated melanoma patients who underwent SLNB. The new 8th edition American Joint Committee on Cancer melanoma staging system T1b category should not be used to determine use of SLNB in thin melanoma, as more than one half of T1b lesions without ulceration have a low risk of positive sentinel lymph nodes.

Sentinel node biopsy for thin melanomas from 2001 to date: 3 different classifications, controversial results

The sentinel node biopsy (SLNB) plays since its introduction in 1992 an indisputable role in the management of melanomas thicker than 1 mm. Its indication is instead debated for "thin" melanomas, with Breslow thickness less than 1 mm (T1), due to the lack of a reliable distinction between melanomas T1a (theoretically at low risk of lymph node metastasis) and T1b melanomas (at higher risk and with indication of sentinel lymph node). From 2001 to date, AJCC has released 3 different staging systems that have identified T1b melanomas with radically different criteria (2001: T1b if Clark higher than or equal to 4; 2009: T1b if mitosis presence; 2017: T1b if Breslow is greater than or equal to 0,8 mm). The presence of ulceration is the only common parameter that identifies T1b stages in all the 3 classification.

Concordance and Reproducibility of Melanoma Staging According to the 7th vs 8th Edition of the AJCC Cancer Staging Manual

The recently updated American Joint Committee on Cancer (AJCC) classification of cancer staging, the AJCC Cancer Staging Manual, 8th edition (AJCC 8), includes revisions to definitions of T1a vs T1b or greater. The Melanoma Pathology Study database affords a comparison,of pathologists' concordance and reproducibility in the microstaging of melanoma according to both the existing 7th edition (AJCC 7) and the new AJCC 8. To compare AJCC 7 and AJCC 8 to examine whether changes to the definitions of T1a and T1b or greater are associated with changes in concordance and reproducibility. In this diagnostic study conducted as part of the national Melanoma Pathology Study across US states, 187 pathologists interpreting melanocytic skin lesions in practice completed 4342 independent case interpretations of 116 invasive melanoma cases. A consensus reference diagnosis and participating pathologists' interpretations were classified into the Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis class IV (T1a) or class V ( T1b) using both the AJCC 7 and AJCC 8 criteria. Concordance with consensus reference diagnosis, interobserver reproducibility, and intraobserver reproducibility. For T1a diagnoses, participating pathologists' concordance with the consensus reference diagnosis increased from 44% (95% CI, 41%-48%) to 54% (95% CI, 51%-57%) using AJCC 7 and AJCC 8 criteria, respectively. The concordance for cases of T1b or greater increased from 72% (95% CI, 69%-75%) to 78% (95% CI, 75%-80%). Intraobserver reproducibility of diagnoses also improved, increasing from 59% (95% CI, 56%-63%) to 64% (95% CI, 62%-67%) for T1a invasive melanoma, and from 74% (95% CI, 71%-76%) to 77% (95% CI, 74%-79%) for T1b or greater invasive melanoma cases. Melanoma staging in AJCC 8 shows greater reproducibility and higher concordance with a reference standard. Improved classification of invasive melanoma can be expected after implementation of AJCC 8, suggesting a positive impact on patients. However, despite improvement, concordance and reproducibility remain low.