Actinic keratosis

• Most common premalignant skin condition.
• Dysplastic proliferations of keratinocytes with a potential for malignant transformation (1).
• Characterized by multifocal scaly, hyperpigmented or scaly lesions, usually brown with a scaly base.
• Histologically they are characterised by marked thickening of the keratin layer (hyperkeratosis) and the prickle cell layer (acanthosis). There may be a variable degree of dysplastic change and abnormal mitotic activity. However the basal layer remains intact.

Note 1 - there is debate whether actinic keratoses are premalignant conditions or alternatively early-stage squamous cell carcinoma (SCC). In a study of 459 patients with cutaneous SCC, there were associated adjacent actinic keratoses in 97% of the cases of cutaneous SCC (2).

Note 2 - there has been tremendous variation in the reported risk of progression of actinic keratosis to invasive SCC (between 0.025% to 16% per year). There is currently no existing technology to distinguish between actinic keratosis lesions that will clear, remain stable, or progress to invasive disease. (3)

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Reference:

• (1) Reinehr CPH, Bakos RM. Actinic keratoses: review of clinical, dermoscopic, and therapeutic aspects. An Bras Dermatol. 2019 Nov-Dec;94(6):637-657. doi: 10.1016/j.abd.2019.10.004. Epub 2019 Nov 6. PMID: 31789244; PMCID: PMC6939186.
• (2) Hurwitz RM, Monger LE. Solar keratosis: an evolving squamous cell carcinoma. Benign or malignant? Dermatol Surg. 1995 Feb;21(2):184. doi: 10.1111/j.1524-4725.1995.tb00141.x. PMID: 7894943.
• (3) Glogau RG. The risk of progression to invasive disease. J Am Acad Dermatol. 2000 Jan;42(1 Pt 2):23-4. doi: 10.1067/mjd.2000.103339. PMID: 10607353.