Prognostic Implication of Lymphovascular Invasion Detected by Double Immunostaining for D2-40 and MITF1 in Primary Cutaneous Melanoma

Utility of PRAME Immunohistochemistry in the Detection of Subtle Melanoma Microsatellites

ABSTRACT

Microsatellitosis is well established as a prognostic factor in malignant melanoma. Its identification leads to subsequent upstaging with implications for further management. We describe 6 cases in which immunohistochemical staining for PReferentially expressed Antigen in MElanoma facilitated detection of small foci of micrometastasis on scanning magnification, which may be potentially missed in routine sections.

Cutaneous Melanomas: A Single Center Experience on the Usage of Immunohistochemistry Applied for the Diagnosis

Cutaneous melanoma (cM) is the deadliest of all primary skin cancers. Its prognosis is strongly influenced by the stage at diagnosis, with early stages having a good prognosis and being potentially treatable with surgery alone; advanced stages display a much worse prognosis, with a high rate of recurrence and metastasis. For this reason, the accurate and early diagnosis of cM is crucial-misdiagnosis may have extremely dangerous consequences for the patient and drastically reduce their chances of survival. Although the histological exam remains the "gold standard" for the diagnosis of cM, a continuously increasing number of immunohistochemical markers that could help in diagnosis, prognostic characterization, and appropriate therapeutical choices are identified every day, with some of them becoming part of routine practice. This review aims to discuss and summarize all the data related to the immunohistochemical analyses that are potentially useful for the diagnosis of cM, thus rendering it easier to appropriately applicate to routine practice. We will discuss these topics, as well as the role of these molecules in the biology of cM and potential impact on diagnosis and treatment, integrating the literature data with the experience of our surgical pathology department.

Hematoxylin and eosin or double stain for CD34/SOX10: Which is better for the detection of lymphovascular invasion in cutaneous melanoma?

BACKGROUND

Lymphovascular invasion (LVI) is considered an unfavorable prognostic factor in cutaneous melanoma (CM). However, its detection by hematoxylin and eosin (H&E) is challenging, with discordant data about its association with clinical-pathological features and no previous studies investigating the inter- (IrOA) and intra-observer (IaOA) agreement. Herein, we tested H&E and double staining (DS) for CD34/SOX10 to detect the LVI in a cohort of 92 CMs, evaluating the IrOA, the IaOA, and the association with the other clinical-pathological features.

METHODS

Five authors independently evaluated 92 consecutive and retrospectively enrolled cases of CMs. We assessed the IrOA (Fleiss's Kappa/FK and intraclass correlation coefficient/ICC) and the IaOA (Cohen's Kappa/CK) with both H&E and CD34/SOX10. Furthermore, we compared the LVI assessment with the two stains and analyzed the association with other clinical-pathological features [χ2 tests for dichotomous and categorical data; Student t-test (normal distribution) and Mann-Whitney U-test (non-normal distribution) for continuous data].

RESULTS

The IrOA was almost identical with H&E (FK=0.446; ICC=0.805) and CD34/SOX10 (FK=0.454; ICC=0.810); by contrast, the IaOA was higher with H&E for one pathologist (CK: 0.809) and with CD34/SOX10 for the other one (CK: 0.563). Applying previously defined criteria, LVI was detected in 10 (9.2%) and 11 (10.1%) cases with H&E and CD34/SOX10, respectively (p = 1.000). Both H&E and CD34/SOX10 were significantly associated with vertical growth phase (H&E, p: 0.014; CD34/SOX10, p: 0.010), mitosis ≥ 1/mm2 (H&E, p: 0.000; CD34/SOX10, p: 0.004), pT (H&E, p: 0.000; CD34/SOX10, p: 0.001), Breslow thickness (H&E, p: 0.000; CD34/SOX10, p: 0.001), and lymph node and/or distant metastasis (H&E, p: 0.005; CD34/SOX10, p: 0.000); only H&E was associated with ulceration (p: 0.002) and distant metastasis (p: 0.000), conversely, only CD34/SOX10 was associated with lymph node metastasis (p: 0.003).

CONCLUSIONS

CD34/SOX10 does not improve the IrOA and the IaOA of the LVI assessment in CM; furthermore, H&E and CD34/SOX10 show a similar profile of association with the other unfavorable clinical-pathological features of CM. As result, CD34/SOX10 could be a redundant diagnostic tool if applied for the prognostic characterization of not-selected CM in a routine diagnostic scenario.

Optimizing Detection of Lymphatic Invasion in Primary Cutaneous Melanoma With the Use of D2-40 and a Paired Melanocytic Marker

ABSTRACT

Dual immunohistochemical (IHC) staining with D2-40 and S100 improves detection of lymphatic invasion (LI) in primary cutaneous melanoma. However, limited data exist evaluating this technique using other melanocytic markers, and thus, the optimal marker for detection of LI is unestablished. To address this knowledge gap, a case-control study was performed comparing melanoma specimens from 22 patients with known lymphatic spread (LS) with a control group of 11 patients without LS. Specimens underwent dual IHC staining with D2-40 and MART-1, SOX-10, and S100 to evaluate for LI. Receiver operating characteristic analysis was used to estimate each stain's accuracy for detection of LI. The LS group was more likely to be ≥65 years (P = 0.04), have a tumor thickness of ≥1 mm (P < 0.01), and have ulcerated tumors (P = 0.02). Detection of LI with D2-40/MART-1 significantly correlated with LS (P = 0.03), and the D2-40/MART-1 stain was most accurate for LI based on receiver operating characteristic curve analysis (area under the curve [AUC] 0.705) in comparison with D2-40/SOX-10 (AUC 0.575) and D2-40/S100 (AUC 0.633). These findings suggest that MART-1 may be the optimal melanocytic marker to combine with D2-40 for detection of LI in melanoma. Further studies are needed to determine the utility of routinely performing these stains for histopathologic analysis of melanoma.

Prognostic Significance of Lymphovascular Invasion Detected by D2-40 in Low-Risk Stage II Colon Cancer

Background

Lymphovascular invasion (LVI) is included in the criteria of high-risk stage II colon cancer. However, there are limitations to detecting LVI by routine hematoxylin and eosin (H&E) staining. Alternatively, immunohistochemistry (IHC) for the lymphatic endothelial marker D2-40 may help detect LVI, but its prognostic significance remains unknown. This study aimed to evaluate the prognostic significance of LVI, detected by IHC for D2-40, in low-risk stage II colon cancer. 

Materials and Methods

A total of 69 patients with low-risk stage II colon cancer were tested for D2-40 to assess LVI. Then, the relationships between IHC-detected LVI and clinical outcomes, including disease-free survival (DFS) and overall survival (OS), were analyzed using both univariate and multivariate analyses. 

Results

IHC for D2-40 revealed that 24 out of the 69 cases (34.78%) had LVI-positive tumors. IHC-detected LVI was significantly associated with adverse clinical outcomes on univariate analysis, i.e., both reduced DFS (P = 0.002) and OS (P = 0.0163). In multivariate analysis, controlling for age, IHC-detected LVI remained a significant predictor of reduced DFS with a hazard ratio (HR) of 3.37 and a 95% confidence interval (CI) of 1.39-8.15 (P = 0.007) and OS (HR, 5.66; 95% CI, 1.02-31.51; P = 0.048).

Conclusions

Our results demonstrated that IHC analysis for D2-40 enhanced LVI detection in patients with low-risk stage II colon cancer and that cases with a missed diagnosis of LVI by routine H&E staining had adverse clinical outcomes, that is, reduced DFS and OS.  

Histopathologic classification and prognostic factors of melanoma: a 2021 update

Despite the rapid recent advances in molecular analysis of tumors, which allow large-scale and high-resolution genomics, the "gold standard" for melanoma diagnosis continues to be histopathology, in conjunction with clinical characteristics and sometimes with important support of immunohistochemistry. Observations, where postulated that cutaneous melanomas may arise through two distinct pathways, discoveries such as that BRAF^V600E mutations were mostly common in melanomas on sun-exposed skin with little solar elastosis and seminal works for melanoma progression and evolution set the groundwork for the new WHO Classification of Melanoma: a classification of melanoma that not only encompasses histologic but also clinical, epidemiologic, and genetic characteristics. The melanomas were divided into those etiologically related to sun exposure and those that are not, based on their mutational signatures, anatomic site, and epidemiology. On the basis of degree of associated solar elastosis melanomas on the sun exposed skin were further divided by the histopathologic degree of cumulative solar damage (CSD) of the surrounding skin, into low and high CSD. On the low-CSD group of melanomas are included superficial spreading melanomas, while the high-CSD melanomas encompasses lentigo maligna and desmoplastic melanomas. The "non-CSD" classification includes acral melanomas, some melanomas in congenital nevi, melanomas in blue nevi, Spitz melanomas, mucosal melanomas, and uveal melanomas. Nodular and nevoid melanoma may occur in any pathway. A group of intermediate tumors termed melanocytoma is proposed for tumors that in addition to mutations that activate the MAPK pathway, harbor multiple driver mutations, and they are either low-grade or high-grade, to indicate that they may carry a higher risk of malignant transformation. In this review a summary of the most recent WHO classification of melanoma is provided. A short analysis of essential histopathologic prognostic parameters is also provided. The new classification of melanoma discriminates distinct types of melanoma based on their clinicopathologic, and genomic characteristics. Undoubtedly, melanoma research will continue to evolve as new clinical, pathological, molecular data accumulates. The challenge of the forthcoming years is to better characterize the intermediate category of melanocytic lesions.

Multiple combinations of melanocytic and vascular endothelial markers enhance the detection rate of lymphovascular invasion in cutaneous melanoma

BACKGROUND

Lymphovascular invasion (LVI) is believed to be the mechanism by which melanoma cells can disseminate to regional lymph nodes and distant sites and may be predictive of adverse outcome. Lymphovascular invasion often difficult to detect on hematoxylin-eosin (HE) stained sections, are readily identified with dual immunohistochemistry (IHC) for melanocytic and vascular markers.

METHODS

A total of 100 primary cutaneous malignant melanoma cases that had a Breslow thickness of 1-4 mm and lacked LVI by conventional HE assessment were included. We compared the LVI detection rates of double staining for CD31/S100 and CD34/S100, and D2-40/S100, and examined the association of LVI with clinical outcomes.

RESULTS

The dual immunohistochemical positivity for CD31/S100, CD34/S100, and D2-40/S100 were 40(40%), 17(17%) and 35(35%), respectively. On multivariate analysis, LVI was an independent predictor of SLN status. Multivariate analysis revealed that LVI and male gender were independent risk factors for overall survival.

CONCLUSIONS

The recognition of LVI is improved by dual IHC and predicts SLN metastasis. The detection of LVI using dual IHC, especially by a combination of CD31/S100 and D2-40/S100 is a useful step that inclusion should be recommended in basic evaluation parameters for cutaneous melanoma.

Lymphatic invasion in acral and non-acral melanoma: a comparative, clinicoprognostic study of primary cutaneous melanoma according to tumour site

There have been limited studies comparing the clinical significance of lymphatic invasion in melanoma according to tumour site. The objective of this study was to evaluate the impact of lymphatic invasion on the clinicoprognostic features of acral and non-acral melanoma. Clinical and histopathological features and survival outcomes of 532 patients with acral melanoma or non-acral melanoma in the database of the Asan Medical Center, Korea, were retrospectively evaluated according to the presence of lymphatic invasion. Lymphatic invasion was significantly more common in acral melanoma than non-acral melanoma. In acral melanoma, lymphatic invasion was significantly associated with a higher frequency of lymph node involvement and advanced stages, but not associated with Breslow thickness or visceral dissemination. By contrast, lymphatic invasion in non-acral melanoma was significantly associated with a higher rate of visceral involvement, deeper Breslow thickness, as well as a higher rate of lymph node involvement and advanced stages. When acral melanoma and non-acral melanoma both with lymphatic invasion were compared, Breslow thickness was significantly shallower and vertical growth phase was significantly less common in acral melanoma. Meanwhile, visceral involvement was significantly more frequent in non-acral melanoma than acral melanoma. In conclusion, lymphatic invasion was more common in acral melanoma than non-acral melanoma and occurred in acral melanoma cases with relatively thin Breslow thickness, suggesting acral melanoma is lymphotropic.

Pathology-based Biomarkers Useful for Clinical Decisions in Melanoma

The dramatic recent advances in therapy of melanoma require a more personalized and precise diagnostic approach to aid in clinical decisions. Tissue-based biomarkers in pathology have diagnostic, prognostic and predictive relevance. Herein we review the most commonly used pathology-based biomarkers in melanoma. Most of these biomarkers are evaluated through immunohistochemistry (IHC) or fluorescent in situ hybridization (FISH) performed on formalin fixed paraffin embedded tissue (FFPE), and are widely available in clinical pathology laboratories. We describe the utility of MART1/Ki67, p16, PRAME, markers of lymphovascular invasion (D2-40, CD31, D2-40/MITF, CD31/SOX-10), BRAF V600E, NRAS, KIT, BAP1, ALK, NTRK, PD-L1, TERT, PTEN, iNOS, and MMR proteins (MLH1, MSH2, MSH6, PMS2) in the evaluation of melanoma specimens. Correct interpretation and awareness of the significance of these biomarkers is crucial for pathologists, dermatologists, and oncologists who take care of melanoma patients.

Associations between the ultrasound features of invasive breast cancer and breast cancer specific survival

AIM

To assess whether ultrasound features of breast cancer are associated with breast cancer specific survival (BCSS).

MATERIALS AND METHODS

Within a single breast service, data was collected prospectively (April 2010-April 2012) from 319 consecutive women (mean age 63 years) with 335 ultrasound-visible invasive breast cancers. Ultrasound features were evaluated retrospectively from the recorded images according to the Breast Imaging Reporting and Data System (BI-RADS) lexicon by a radiologist blinded to outcomes. Survival and cause of death were ascertained from local and national sources. Kaplan-Meier survival curves were generated, and statistical significance tested using the log-rank test.

RESULTS

Mean follow-up in those alive was 80.9 months. Thirty breast cancer deaths and 45 non-breast cancer deaths occurred. Five-year BCSS in the presence of distal acoustic enhancement was 76% compared to 88%, 96%, and 100% for those with distal shadowing, no distal effect or combined effect respectively (p<0.0002). Patients with sonographic skin involvement had 73% 5-year BCSS compared to 92% for no skin involvement (p<0.0001). Focal oedema was associated with 56% 5-year BCSS compared to 89% for those without (p=0.0002). A significant association was demonstrated between ultrasound tumour size and BCSS (p<0.0001). At multivariate analysis, skin changes, distal enhancement, and focal oedema maintained prognostic significance.

CONCLUSION

Distal enhancement, focal oedema, and skin involvement have strong associations with breast cancer death. These factors could be taken into account, along with lesion size and other commonly used preoperative prognostic features, when considering management of women with breast cancer.

Pathology of Melanoma

Melanoma is an aggressive malignancy arising from melanocytes in the skin and rarely in extracutaneous sites. The understanding of pathology of melanoma has evolved over the years, with the initial classifications based on the clinical and microscopic features to the current use of immunohistochemistry and genetic sequencing. The depth of invasion and lymph node metastasis are still the most important prognostic features of melanoma. Other important prognostic features include ulceration, lymphovascular invasion, mitosis, and tumor-infiltrating lymphocytes. This article reviews the pathology of melanoma and its precursor lesions, along with the recent advances in pathologic diagnosis of melanoma.

Guidelines of care for the management of primary cutaneous melanoma

The incidence of primary cutaneous melanoma continues to increase each year. Melanoma accounts for the majority of skin cancer-related deaths, but treatment is usually curative following early detection of disease. In this American Academy of Dermatology clinical practice guideline, updated treatment recommendations are provided for patients with primary cutaneous melanoma (American Joint Committee on Cancer stages 0-IIC and pathologic stage III by virtue of a positive sentinel lymph node biopsy). Biopsy techniques for a lesion that is clinically suggestive of melanoma are reviewed, as are recommendations for the histopathologic interpretation of cutaneous melanoma. The use of laboratory, molecular, and imaging tests is examined in the initial work-up of patients with newly diagnosed melanoma and for follow-up of asymptomatic patients. With regard to treatment of primary cutaneous melanoma, recommendations for surgical margins and the concepts of staged excision (including Mohs micrographic surgery) and nonsurgical treatments for melanoma in situ, lentigo maligna type (including topical imiquimod and radiation therapy), are updated. The role of sentinel lymph node biopsy as a staging technique for cutaneous melanoma is described, with recommendations for its use in clinical practice. Finally, current data regarding pregnancy and melanoma, genetic testing for familial melanoma, and management of dermatologic toxicities related to novel targeted agents and immunotherapies for patients with advanced disease are summarized.

Intratumoral and peritumoral lymphovascular invasion detected by D2-40 immunohistochemistry correlates with metastasis in primary cutaneous Merkel cell carcinoma

Primary cutaneous Merkel cell carcinoma (MCC) is an aggressive neuroendocrine malignancy in which lymphovascular invasion (LVI) correlates with more aggressive phenotype. The prognostic significance of LVI detected by D2-40 immunohistochemistry (IHC) in MCC remains controversial. We aimed to determine how LVI detected by D2-40 IHC compares with LVI detected by hematoxylin and eosin (H&E) staining in predicting MCC metastasis. Clinical and histopathologic features of MCCs diagnosed and treated in 2002 to 2015 were assembled and included 58 MCC tumors from 58 patients. H&E-stained tissue sections and D2-40 IHC studies were reviewed. When LVI was present, the location (peritumoral or intratumoral) and the size of the largest invaded vessel were recorded. LVI findings by H&E staining and D2-40 IHC were compared with each other and with histologic features and clinical outcomes. H&E staining showed LVI in 37 of 58 cases; D2-40 IHC confirmed LVI in 30 of these cases but failed to confirm LVI in 7. D2-40 IHC also detected 14 cases of LVI not identified on H&E staining. Histologically, D2-40-detected LVI was associated with infiltrative growth pattern and nonbrisk lymphoid infiltrate (P = .005 and P = .055, respectively). There was a statistically significant difference between the frequency of detection of peritumoral LVI by H&E in comparison to D2-40 IHC (P = .0009). MCCs in which D2-40 IHC-detected both intratumoral and peritumoral LVI were typically larger than MCCs without (mean, 24.5 mm versus 17.3 mm; P = .03) and more frequently metastasized (87% versus 51%; P = .03). D2-40 IHC detection of both intratumoral and peritumoral LVI is associated with metastasis.

Clinical impact of ulceration width, lymphovascular invasion, microscopic satellitosis, perineural invasion, and mitotic rate in patients undergoing sentinel lymph node biopsy for cutaneous melanoma: a retrospective observational study at a comprehensive cancer center

The prognostic significance of the width of the ulceration in primary melanomas remains unclear, and there is a relative paucity of data for lymphovascular invasion (LVI), microscopic satellitosis (MS), perineural invasion (PNI), and mitotic rate when compared with other pathological elements currently required for reporting. To evaluate the prognostic importance of the ulceration width and other important pathologic measurements, a single-institutional retrospective study was conducted using records of cutaneous melanoma patients who underwent sentinel lymph node (SLN) biopsy at The University of Texas, MD Anderson Cancer Center between 2003 and 2008. We identified 1898 eligible patients with median tumor thickness of 1.25 mm and median follow-up of 6.7 years. By multivariable analyses, the strongest risk factor for SLN positivity was high tumor thickness followed by the presence of LVI. The pathologic measures with the strongest influence on recurrence-free survival (RFS) were tumor thickness and positive SLN status. Ulceration width and presence of MS were also significantly associated with RFS while PNI was not. Factors with the strongest influence on melanoma-specific survival (MSS) were positive SLN status and mitotic rate. In conclusion, SLN biopsy should probably be offered if the primary tumor has LVI. MS is an adverse prognostic factor for RFS, but its influence on outcome is modest. Ulceration width predicts RFS but loses its independent prognostic significance for MSS when adjusting for currently used clinicopathological factors. In view of its impact on MSS, mitotic rate should be recorded for cutaneous invasive melanomas across all T categories.

Lymphatic invasion and the Shields index in predicting melanoma metastases

INTRODUCTION

Findings of the prognostic significance of lymphatic invasion are contradictory. To determine an as efficient cutaneous melanoma metastasis predictor as possible, Shields et al. created a new prognostic index. This study aimed to examine whether the lymphatic invasion analysis and the Shields index calculation can be used in predicting lymph node status in patients with cutaneous melanoma.

METHODS

Lymphatic invasion of 100 melanoma specimens was detected by dual immunohistochemistry staining for the lymphatic endothelial marker D2-40 and melanoma cell S-100 protein. The Shields index was calculated as a logarithm by multiplying the melanoma thickness, square of peritumoural lymphatic vessel density and the number "2" for the present lymphatic invasion.

RESULTS

No statistically significant difference was observed between lymph node metastatic and nonmetastatic melanomas regarding the lymphatic invasion. Metastatic melanomas showed a significantly higher Shields index value than nonmetastatic melanomas (p = 0.00). Area under the receiver operator characteristic (ROC) curve (AUC) proved that the Shields index (AUC = 0.86, 95% confidence interval (CI) 0.79-0.93, p = 0.00) was the most accurate predictor of lymph node status, followed by the melanoma thickness (AUC = 0.76, 95% CI 0.67-0.86, p = 0.00) and American Joint Committee on Cancer (AJCC) staging (AUC = 0.75, 95% CI 0.66-0.85, p = 0.00), while lymphatic invasion was not successful in predicting (AUC = 0.56, 95% CI 0.45-0.67, p = 0.31). The Shields index achieved 81.3% sensitivity and 75% specificity (cut-off mean value).

CONCLUSIONS

Our findings show that D2-40/S-100 immunohistochemical analysis of lymphatic invasion cannot be used for predicting the lymph node status, while the Shields index calculation predicts disease outcome more accurately than the melanoma thickness and AJCC staging.

Lymphatic invasion predicts sentinel lymph node metastasis and adverse outcome in primary cutaneous melanoma

BACKGROUND

Sentinel lymph node (SLN) metastasis is a powerful predictor of survival in primary cutaneous melanoma. Lymphatic invasion (LI) may correlate with increased risk of SLN metastasis. Intralymphatic metastases, often difficult to detect on hematoxylin and eosin (H&E) stained sections, are readily identified with dual immunohistochemistry for melanocytic and lymphatic markers.

METHODS

We used dual S100/D240 immunohistochemistry to detect LI in 125 melanomas from patients who underwent SLN biopsy and correlated LI with melanoma staging parameters and disease status.

RESULTS

Dual immunohistochemistry allowed for the identification of LI in 33 cases (26%), compared to only 2% on H&E stained sections. Melanomas with LI showed greater thickness, higher mitotic rate and more frequent ulceration. Eleven of 33 cases with LI (33%) and 10 of 92 cases without LI (11%) were associated with a positive SLN (P = .006). More patients without LI were disease-free at last follow-up (80%) than patients with LI (50%; P = .002); LI was significantly associated with decreased progression-free survival.

CONCLUSION

The detection of LI is improved by dual immunohistochemistry and predicts SLN metastasis. The presence of LI may impact therapeutic planning in melanoma, such as the decision to perform a SLN biopsy.

Lymphatic invasion and angiotropism in primary cutaneous melanoma

Access of melanoma cells to the cutaneous vasculature either via lymphatic invasion or angiotropism is a proposed mechanism for metastasis. Lymphatic invasion is believed to be a mechanism by which melanoma cells can disseminate to regional lymph nodes and to distant sites and may be predictive of adverse outcomes. Although it can be detected on hematoxylin- and eosin-stained sections, sensitivity is markedly improved by immunohistochemistry for lymphatic endothelial cells. Multiple studies have reported a significant association between the presence of lymphatic invasion and sentinel lymph node metastasis and survival. More recently, extravascular migratory metastasis has been suggested as another means by which melanoma cells can spread. Angiotropism, the histopathologic correlate of extravascular migratory metastasis, has also been associated with melanoma metastasis and disease recurrence. Although lymphatic invasion and angiotropism are not currently part of routine melanoma reporting, the detection of these attributes using ancillary immunohistochemical stains may be useful in therapeutic planning for patients with melanoma.

Tumor Thickness and Mitotic Rate Robustly Predict Melanoma-Specific Survival in Patients with Primary Vulvar Melanoma: A Retrospective Review of 100 Cases

Purpose: Primary vulvar melanoma (PVM) is the second most common vulvar malignancy. Despite their distinct anatomic site and unique molecular-genetic alterations, PVMs are staged according to the American Joint Committee on Cancer (AJCC) guidelines for primary cutaneous melanomas (PCM). However, whether parameters derived for PCM also apply to PVM remain a critical yet largely unexplored clinical question. The objective of this study was to determine the parameters predictive of survival in PVM.Experimental Design: We retrospectively reviewed 100 patients with PVM and determined associations between clinical and histopathologic parameters and disease-specific survival (DSS) and overall survival (OS).Results: Univariate Cox regression analysis demonstrated older age (>56 years), greater tumor thickness, higher dermal mitotic rate, ulceration, lymphovascular invasion, perineural invasion, microscopic satellitosis, and absence of precursor nevus associated with decreased OS. Furthermore, age, midline, and/or multifocal involvement, greater tumor thickness, higher dermal mitotic rate, ulceration, lack of regression, lymphovascular invasion, perineural invasion, and microscopic satellitosis associated with decreased DSS. Multivariate analysis demonstrated tumor thickness, dermal mitotic rate, lymphovascular invasion, microscopic satellitosis, and absence of precursor nevus independently predicted shorter OS. Only tumor thickness and increased dermal mitotic rate (≥2/mm²) independently predicted reduced DSS. In comparison with the AJCC T-category, a novel, bivariate T-category based only on tumor thickness and dermal mitotic rate robustly predicted OS and DSS in our patient cohort.Conclusions: In the largest single institutional study of PVM, we demonstrate a combination of tumor thickness and mitotic rate comprise a simple but robust T-category to direct staging and prognosis. Clin Cancer Res; 23(8); 2093-104. ©2016 AACR.