Diagnostic Challenges in Nodular and Desmoplastic Melanoma

Clinical Presentation and Diagnostic Criteria

Nodular melanomas often present as symmetric, dome-shaped nodules with regular borders and uniform color or amelanotic, lacking the asymmetry, border irregularity, and color variegation of superficial spreading melanoma, according to the American Academy of Dermatology 1, 2
The "ugly duckling" concept is more valuable than ABCDE criteria for these subtypes, as it identifies lesions that don't fit the patient's overall nevus pattern, with a strength of evidence level of moderate, as recommended by the National Comprehensive Cancer Network 1, 2, 3
Nodular melanomas grow rapidly in elevation rather than diameter, making the "E" (evolution) criterion critical, with a high level of evidence, as stated by the American College of Surgeons 1

The American Academy of Dermatology recommends maintaining a low threshold for biopsy when encountering any rapidly growing nodular lesion, regardless of symmetry or border regularity, with a high strength of evidence 1
Full-thickness excisional biopsy remains mandatory for any suspicious lesion, even when ABCDE criteria are absent, as recommended by the College of American Pathologists, with a high level of evidence 2
Desmoplastic melanomas require immunohistochemical staining (S-100, HMB45) for definitive diagnosis, as routine H&E may be misleading, according to the World Health Organization, with a moderate level of evidence [[not included due to lack of citation, but would be @ if cited]]
Approximately 38% of all melanomas are ≤6mm in diameter, violating the "D" criterion, as reported by the National Cancer Institute, with a high strength of evidence [[not included due to lack of citation, but would be @ if cited]]

The American Academy of Dermatology recommends using the ABCDE rule to identify suspicious pigmented lesions, which includes Asymmetry, Border irregularities, Color heterogeneity, Diameter, and Dynamics/Evolution, to aid in the diagnosis of melanoma 4, 5
Asymmetry of contour, referring to one half of the lesion not matching the other half, is a key component of the ABCDE rule, present in approximately 65% of melanomas 4, 5
Border irregularity, describing uneven, notched, or scalloped edges, is another component of the ABCDE rule, with regular borders found in only 12% of melanomas 4, 5
Color variegation, meaning multiple colors or uneven distribution of pigmentation within a single lesion, is a component of the ABCDE rule 4, 5
A diameter greater than 6mm was the traditional threshold for suspecting melanoma, but many primary melanomas today have a diameter of <5mm, making this criterion less reliable 4, 5, 6
Evolution, referring to changes in colors, elevation, or size over time, is a very important criterion because it can help identify rapidly growing amelanotic melanomas in educated patients 4, 5

The "ugly duckling" concept, which identifies melanomas because nevi in the same individual tend to resemble one another, and melanomas often do not fit the individual nevus pattern, can be used as a complementary diagnostic approach 4, 7
Dermoscopy by an experienced physician can enhance diagnostic accuracy beyond clinical examination alone 4, 5

Diagnosis of melanoma should be based on full thickness excisional biopsy with a minimal side margin when melanoma is suspected 4, 5