Variability in the Histopathological Diagnosis of Non-Melanocytic Lesions Excised to Exclude Melanoma

Abstract

Introduction: The differential diagnosis of lesions excised to exclude melanoma include a variety of benign and malignant melanocytic and non-melanocytic lesions.

Objectives: We examined the variability between pathologists in diagnosing non-melanocytic lesions.

Methods: As part of a larger study prospectively examining the diagnosis of lesions excised to exclude melanoma in 198 patients at a primary care skin cancer clinic in Newcastle, Australia, we compared diagnosis made by 5 experienced dermatopathologists, of 44 non-melanocytic lesions in 44 patients aged 22-90.

Results: Forty-four lesions (out of 217 in total) were non-melanocytic. Among the 5 pathologists who examined each case there was marked variability in the terminology used to diagnose each case. The most common variability was found between seborrheic keratosis, large cell acanthoma, solar lentigo, and lichenoid keratosis. The diagnosis made by the majority of the pathologists was deemed to be the reference diagnosis. Versus majority diagnosis, 4% of benign lesions were considered malignant, and 7% of malignant diagnoses were considered as benign.

Conclusions: The different terminology adopted and lack of consensus in the diagnosis of these non-melanocytic lesions in this setting suggests that training AI systems using gold standards may be problematic. We propose a new management classification scheme called MOLEM (Management of Lesions Excised to exclude Melanoma) which expands the previously described MPATH-dx to include non-melanocytic lesions.

Keywords: AI; artificial intelligence; diagnosis; large cell acanthoma; melanoma; seborrheic keratosis.

Figure 1

(A) Clinical image showing a solitary asymmetric pigmented macule in sun-damaged skin of upper back. (B) Dermoscopy shows central brown dots and grey areas, and at 6–9 o’clock possible abnormal network with rhomboidal structures, and at 1–3 o’clock features of regression. (C) Stained pathology slide (H&E, ×20), cropped from the Pathpresenter WSI shows slightly thickened epidermis but with minimal cytologic atypia and most pigment in basal keratinocytes. This is a link to the WSI: https://pathpresenter.net/#/public/display?token=34352199.

Figure 2

Lesion unanimously diagnosed as solar lentigo. (A) Clinical and (B) dermoscopic images show broad lentiginous pigment with some asymmetry and a possible abnormal network. (C) Pathology (H&E, ×20), showing bulbous acanthosis of epidermis hyperkeratosis increased basal pigmentation, mainly in keratinocytes. The WSI images are found at https://pathpresenter.net/#/public/display?token=1d8609e3.

Figure 3

Lesion that was either defined as lichenoid keratosis, intra-epidermal squamous cell carcinoma, or seborrheic keratosis by pathologists participating to this study. (A) Clinical image shows an asymmetrical lesion with red/pink and brown within sun damaged skin. (B) Dermoscopy shows a pink and brown, traumatized lesion, possible peripheral network, and central inflammation. (C) Dense lichenoid chronic inflammatory infiltrate with interface change with some squamous atypia that for some pathologists was diagnostic for intra-epidermal squamous cell (H&E, ×10). (D) SOX-10 immunohistochemistry (magnification 10x) with no significant increase in melanocytes. The WSI image of the H&E can be found at https://pathpresenter.net/#/public/display?token=0c88e847.