Actinic keratosis with atypical basal cells (AK I) is the most common lesion associated with invasive squamous cell carcinoma of the skin

Abstract

Direct invasion from proliferating basaloid atypical keratinocytes limited to the epidermal basal layer (AK I), known as the differentiated pathway, was the most common form of progression to cutaneous iSCC in our series. On the other hand, stepwise progression from AK I to AK II and AK III (classic pathway) was seen to be operative in a substantial proportion of iSCC cases. All AK lesions, irrespective of intraepidermal neoplasia thickness, are therefore potentially invasive and tumour advance along adnexal structures might facilitate iSCC development from AK I lesions.

A review of BF-200 ALA for the photodynamic treatment of mild-to-moderate actinic keratosis

“…In general patients develop multiple AKs in one area and predicting which course each individual lesion will follow is impossible. Nonetheless, AK lesions are reliable markers for patients who are most predisposed to developing invasive SCC [4,[12][13].AK lesions typically appear in areas most frequently exposed to the sun such as the face, back of the hands, or bald scalp; 75% of lesions are found on the head, neck and forearms [14]. The lesions vary in appearance as well as size and can include erythematous scaly macules, rough pigmented patches and hyperkeratotic skin horns.…”

“…In general patients develop multiple AKs in one area and predicting which course each individual lesion will follow is impossible. Nonetheless, AK lesions are reliable markers for patients who are most predisposed to developing invasive SCC [4,[12][13].…”

“…Approximately 65% of all primary SCCs develop from lesions previously diagnosed as AK [29]. The remainders most likely develop from subclinical AK lesions in cancerized fields [12]. Thus, in order to prevent disease progression, it is strongly advised to treat AK with all diligence independent of severity [16].…”

“…These can potentially sustain and aggravate the disease state, if only visible lesions are treated [26,27]. In addition, it has been shown that mild AKs (grade I) are the most common lesion associated with invasive SCC [12,13]. Since there are no defined clinical indicators or specific genetic markers to predict progression to SCC, the expert opinion is to administer AK treatment in a field-directed manner in all patients to prevent invasive SCCs [28].…”

Preventive treatment of sun-damaged skin: Topical treatment of actinic keratosis can prevent surgery in non-melanoma-skin-cancer

“…They slowly progress to invasive squamous cell carcinoma by the ability to grow in three dimensions: (1) horizontal growth along the basal cell layer, or (2) vertical growth in two directions either "upwards" within the epidermis, or (3) "downwards" invading papillary dermal layers [1,2] (Figure 1). There is no chronological order within these three growingdirections and AK may therefore become invasive at all stages of progression (AK 1, AK 2, or AK3) [3].…”