Pathway to clarity simplified: Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis (MPATH-Dx) version 2.0

By Jason B. Lee, MD, FAAD
July 16, 2025
Vol. 7, No. 28

In modern medical practice, clinical care guidelines have emerged to promote consistent and evidence-based practices to manage common diseases. In dermatology, the American Academy of Dermatology, in collaboration with the National Psoriasis Foundation, has published clinical guidelines for treating psoriasis. (1) The guidelines offer clinicians a framework to deliver standardized care to improve patient outcomes, enhance safety, and reduce wasted resources. The recent standardized laboratory monitoring for isotretinoin serves as an example of the emergence of newly evidence-based care guidelines that significantly impacted the unnecessary laboratory monitoring practices of the past. (2,3)

Despite the increasing availability of formal clinical care guidelines, clinical management and treatment for many common skin conditions still lack support from standardized, evidence-based clinical care guidelines. The management and treatment of melanocytic neoplasms exemplify this issue, where a standardized approach is lacking, often leading to variation in their management. While organizations such as the American Joint Committee on Cancer and the National Comprehensive Cancer Network regularly update formal staging, management, and treatment guidelines for melanoma, no such guidelines exist for a large group of melanocytic neoplasms encountered by dermatologists. The clinical management of these lesions may vary depending on the local practice culture and the clinician’s belief about the nature of the lesions, which may vary depending on the training background. Furthermore, for some melanocytic neoplasms, the lack of standardized diagnostic terms and disagreements about their fundamental nature have contributed to the inconsistent varied management among clinicians. For example, initially described as B-K mole by Clark and colleagues, this nevus has been referred to as dysplastic nevus, atypical nevus, nevus with architectural disorder, and Clark nevus. Treatment decisions for this nevus can range from no action to aggressive management, depending on the clinician’s and pathologist’s perceived risk of melanoma. Similarly, the management of Spitz nevus also varies as some pediatric dermatologists leave it alone while others consistently opt for complete excision.

In 2014, the MPATH-Dx schema was introduced to simplify and standardize the reporting of melanocytic neoplasms by categorizing them into five classes. (4) The schema provides the risk of progression to melanoma and treatment recommendations regardless of the different diagnostic terms used. The classification schema is modeled after the successful implementation of a standardized classification system in radiology for interpreting and reporting mammography, ultrasound, and MRI findings, referred to as the Breast Imaging-Reporting and Data System (BI-RADS). (5) For the lesions in Classes I and V in the initial MPATH-Dx schema, there is little disagreement or controversy in the risk assignment and management, as they represent the benign and malignant ends of the spectrum, respectively. (Table 1) For the lesions in Classes II and III, however, some authors have expressed concerns about overtreatment and overmonitoring. (6,7) They point out that conventional Spitz nevi, cellular blue nevi, and Reed nevi, categorized into the Class II group, are benign lesions and their removal should not be routine, especially because they often occur in cosmetically sensitive areas or difficult-to-remove sites in children. For Spitz nevi and special site nevi, the excision recommendation may not necessarily be due to an inherently higher risk of progression to melanoma but rather because of the diagnostic challenges and a higher likelihood of histopathologic misdiagnosis. Additionally, the inclusion of melanoma in situ in the Class III group may surprise some as the definitive diagnosis of malignancy, albeit in situ, is included with atypical lesions where progression risk is not clearly defined or unknown.

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The Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis Version 1.0

MPATH-Dx Class	Risk of tumor progression	Treatment recommendation	Examples (partial list)
I	No risk for progression to melanoma	No further treatment	Atypical/dysplastic nevi with mild atypia Common blue nevi Congenital nevi, no atypia
II Low grade	Low risk for progression to melanoma	Complete excision narrow margins (<0.5 cm)	Atypical/dysplastic nevi with moderate atypia Cellular blue nevi Conventional Spitz nevi and Reed nevi Deep penetrating nevi Special site nevi (acral, groin, breast, scalp)
III High grade	Higher risk for progression to melanoma	Complete excision 0.5 cm to <1 cm margins	Atypical/dysplastic nevi with severe atypia Atypical Spitz tumors Melanoma in situ
IV Melanoma pT1a	Low risk for metastasis	Follow melanoma guideline	Melanoma <0.8 mm Breslow thickness
V Melanoma ≥pT1b	Moderate risk for metastasis	Follow melanoma guideline	Melanoma ≥0.8 mm Breslow thickness

Adopted from Piepkorn MW et al. (Ref 4). For a complete listing of examples, refer to the reference.

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The authors of the MPATH-Dx schema recognize that clinicians have differing views on the melanoma risk of progression for lesions in Class II and III and that the treatment recommendation is not evidence-based. They offer the diagnosis-treatment mapping schema to supplement conventional reporting to reduce the current ambiguity and confusion among clinicians and patients. They offer this schema as a foundational framework for continued dialogue on risk assessment and treatment approaches for melanocytic neoplasms.

To that end, in early 2023, a new version of MPATH-Dx version 2.0 was published after years of feedback, aligning with the 2018 WHO classification of melanocytic neoplasm. (8) The revised schema simplifies the original five classes into four. (Table 2) In the new schema, nevi with a low-grade atypia designation belongs to Class I and has no further treatment recommendation. In contrast, any nevi with a high-grade atypia designation belongs to Class II with an excision recommendation with 1 cm margins. Spitz nevi, cellular blue nevi, and deep penetrating nevi continue to be classified as high-risk lesions, and thus, they are included in Class II. The margin recommendation of up to 1 cm may be seen as vague, arbitrary, and too aggressive for Class II lesions by many clinicians, who seek more precise margins as the surgeries may significantly negatively impact patients, depending on the site and patient’s age. Another issue raised is the potential for pathologists to overutilize high-grade categories for lesions with any degree of diagnostic uncertainty to mitigate potential liability. (7) Pathologists are under significant pressure to accurately classify melanocytic neoplasms given the severe consequences of missing a melanoma. This environment contributes to the tendency for pathologists to lower the threshold and upgrade lesions as atypical or high grade, which leads to preferential removal of melanocytic lesions over conservative management. (9)

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The Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis Version 2.0

MPATH-Dx Class 2.0	Risk of tumor progression	Treatment recommendation	Examples (partial list)
I Low grade	Very low risk for progression to melanoma	No further treatment	Atypical/dysplastic nevi, low-grade atypia Common blue nevi Congenital nevi, no atypia
II High grade	Low risk for progression to invasive melanoma	Complete excision <1 cm margins	Atypical/dysplastic nevi, high grade atypia Cellular blue nevi or melanocytomas Spitz nevi, Reed nevi Atypical Spitz tumors Deep penetrating nevi Special site nevi (acral, groin, breast, scalp) Melanoma in situ
III Melanoma pT1a	Low risk for metastasis	Follow melanoma guideline	Melanoma <0.8 mm Breslow thickness
IV Melanoma ≥pT1b	Moderate risk for metastasis	Follow melanoma guideline	Melanoma ≥0.8 mm Breslow thickness

Adopted from Barnhill RL et al. (Ref 8). For a complete listing of examples, refer to the reference.

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The ultimate measure of the success of the MPATH-Dx schema is improved patient outcomes while minimizing the harms of overdiagnosis and overtreatment. Fundamental to the success of the schema is consistency among pathologists in accurately categorizing melanocytic lesions within its framework. In the largest iteration of the concordance rate study among pathologists using the MPATH-Dx version 1.0 schema, while the concordance rates for the two ends of the diagnostic spectrum were good, they dropped to 25% for Class II lesions and 40% for Class III lesions that included atypical/dysplastic nevi, Spitz nevi, atypical Spitz tumor, and melanoma in situ. (10) The low rates underscore the subjective nature of the gold standard in diagnosing melanocytic neoplasms and the urgent need for improving diagnostic consistency among pathologists. Addressing these concordance issues is crucial and should proceed in parallel with implementing the MPATH-Dx schema to ensure its success and effectiveness.

The authors of MPATH have taken bold first steps, working toward more precise classification, clarity in management, and standardization of reporting melanocytic neoplasms. They have created a foundational framework that paves the way for refining and improving the diagnostic and treatment pathways for melanocytic neoplasms, a feat for which they should be highly commended.

Point to Remember: Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis (MPATH-Dx) is a diagnostic-treatment schema designed to standardize the classification, reporting, and treatment of melanocytic neoplasms. The success of the schema depends on the continual engagement and contribution of clinicians and pathologists by sharing their insights and expertise.

Our expert’s viewpoint

Daniel Lozeau, MD, FAAD
Departments of Dermatology and Pathology
Stony Brook University

In his comment on version 2.0 of the Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis (MPATH-Dx), Jason Lee succinctly highlights the intended usage and benefits of the schema, as well as some of the obstacles to its widespread adoption. When used consistently, the tool has the potential to stimulate conversation between dermatologists and pathologists, resulting in a better shared understanding of the expected biological behavior of melanocytic lesions. Part of this understanding is acknowledging that some melanocytic lesions are difficult to classify. A brief review of the modern dermatopathology literature reveals a vocabulary to describe these difficult lesions that has proliferated much like the melanocytes they describe: atypical intraepidermal melanocytic proliferation (AIMP), intraepidermal borderline melanocytic tumor (IBMT), de novo intraepidermal melanocytic dysplasia (DNIMD), pagetoid melanocytic proliferation (PMP), superficial atypical melanocytic proliferation of uncertain significance (SAMPUS), melanocytic tumor of uncertain malignant potential (MELTUMP)… The list goes on, without even scratching the surface of dysplastic nevi terminology.

The abundance of terms highlights the lack of concordance among pathologists in diagnosing melanocytic lesions, but also highlights the usefulness of MPATH-Dx to overcome this. At the end of the day, dermatologists care more about how to treat a particular lesion than about the specific jargon used by their pathologist to describe it. As a dermatopathologist, I can admit that I often know whether (in my opinion) a lesion should be re-excised before I know the specific language that I am going to use in my report. MPATH-Dx does away with any potential confusion that my report may create — under the current version 2.0 schema, these lesions are all Class II, high-grade tumors that should be excised with < 1 cm margins.

As noted by Lee, reasonable minds could differ over the inclusion of specific diagnoses in specific categories (for example: do Spitz/Reed nevi and special site nevi belong in Class II or Class I?). The creation of the MPATH-Dx categories was accomplished via a modified Delphi approach among a panel of three expert dermatopathologists. Herein lies an opportunity to improve further on the foundation set by MPATH-Dx v2.0; namely, the opportunity to use evidence-based medicine guidelines to more strictly evaluate in which category uncertain melanocytic lesions belong. Ten years ago, the tide began to turn on the management of dysplastic nevi, and today it is widely accepted that the vast majority of these lesions are benign and require no further attention. Ideally, the next iteration of MPATH-Dx would further refine the categories set forth in version 2.0, affording an opportunity to spare even more patient and physician anxiety, surgical morbidity, and health care dollars.

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References

1. American Academy of Dermatology. Psoriasis Clinical Guideline. Accessed Oct 24, 2024. https://staging.aad.org/member/clinical-quality/guidelines/psoriasis

2. Xia E, Han J, Faletsky A, et al. Isotretinoin Laboratory Monitoring in Acne Treatment: A Delphi Consensus Study. JAMA Dermatol. 2022;158(8):942-948. doi:10.1001/jamadermatol.2022.2044

3. Hansen TJ, Lucking S, Miller JJ, Kirby JS, Thiboutot DM, Zaenglein AL. Standardized laboratory monitoring with use of isotretinoin in acne. J Am Acad Dermatol. 2016;75(2):323-328. doi:10.1016/j.jaad.2016.03.019

4. Piepkorn MW, Barnhill RL, Elder DE, et al. The MPATH-Dx reporting schema for melanocytic proliferations and melanoma. J Am Acad Dermatol. 2014;70(1):131-141. doi:10.1016/j.jaad.2013.07.027

5. Burnside ES, Sickles EA, Bassett LW, et al. The ACR BI-RADS experience: learning from history. J Am Coll Radiol. 2009;6(12):851-860. doi:10.1016/j.jacr.2009.07.023

6. Elston DM. Management of atypical pigmented lesions. J Am Acad Dermatol. 2014;70(1):142-145. doi:10.1016/j.jaad.2013.08.003

7. Clarke LE, Hosler GA. A standardized approach to classifying melanocytic neoplasms? Comments on the MPATH-Dx system. J Cutan Pathol. 2021;48(6):730-732. doi:10.1111/cup.13994

8. Barnhill RL, Elder DE, Piepkorn MW, et al. Revision of the Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis Classification Schema for Melanocytic Lesions: A Consensus Statement. JAMA Netw Open. 2023;6(1):e2250613. Published 2023 Jan 3. doi:10.1001/jamanetworkopen.2022.50613

9. Welch HG, Mazer BL, Adamson AS. The Rapid Rise in Cutaneous Melanoma Diagnoses. N Engl J Med. 2021;384(1):72-79. doi:10.1056/NEJMsb2019760

10. Elmore JG, Barnhill RL, Elder DE, et al. Pathologists' diagnosis of invasive melanoma and melanocytic proliferations: observer accuracy and reproducibility study [published correction appears in BMJ. 2017 Aug 8;358:j3798. doi: 10.1136/bmj.j3798]. BMJ. 2017;357:j2813. Published 2017 Jun 28. doi:10.1136/bmj.j2813

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