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Summary Background We have previously observed that persistent activation of the serine/threonine kinase, protein kinase B (AKT) is a frequent event in extramammary Paget’s disease (EMPD). AKT promotes cell proliferation by its ability to coordinate mitogenic signalling with energy- and nutrient-sensing pathways that control protein synthesis through the atypical serine/threonine kinase, mammalian target of rapamycin (mTOR). CDK2, a member of the serine/threonine kinase family of cyclin-dependent kinases, is a key regulator of G1–S cell cycle progression, and has recently been shown to be one of the targets of AKT. The AKT–mTOR–p70 ribosomal protein S6 kinase (p70S6K) pathway has been described in some human malignancies, but not in EMPD. Objective To investigate the immunohistochemical staining of the AKT–mTOR–p70S6K pathway in EMPD and to evaluate the relationships among the components. Methods Samples of primary EMPD tissue were subjected to immunohistological staining with phosphorylated (p)-AKT, p-mTOR, p-4E-binding protein 1 (p-4EBP1), p-p70S6K/S6K1, p-ribosomal protein S6 (p-S6) and CDK2. Ten normal skin samples served as a control. Results Of the 32 EMPD tissue samples, 29, 27, 26, 29, 26 and 32 samples were positive for p-AKT, p-mTOR, p-4EBP1, p-p70S6K/S6K1, p-S6 and CDK2 staining, respectively. All these cell signalling molecules showed higher positivity in invasive EMPD than in EMPD in situ. There were significant correlations between p-AKT, p-mTOR, p-4EBP1, p-p70S6K/S6K1 and p-S6 and CDK2. Conclusions The activation of the AKT–mTOR–p70S6K pathway may play an important role in the pathogenesis of EMPD. The high expression of the components of the pathway was highly correlated with CDK2 expression, suggesting that the AKT/mTOR pathway may induce the malignant transition through CDK2 in EMPD. The AKT–mTOR–p70S6K pathway might be a potential therapeutic target in EMPD.

Cytokeratin 19 (CK19) has been considered to be a putative marker for epidermal stem cells in the hair follicle bulge. Cumulative reports have shown that epidermal stem cells play an important role in skin carcinogenesis. However, to date there has been no report on the clinical alteration of the stem cells in squamous cell carcinoma (SCC).To investigate alteration of the stem cells and proliferating cells and to assess their relationship and potential contribution to SCC.Thirty paraffin-embedded neoplastic skin lesions, consisting of 10 cases each of actinic keratosis (AK), Bowen disease (BD) and SCC, were examined immunohistologically for CK19 and Ki-67.Positive reactivity for CK19 was seen in 30% of AK, 50% of BD and 80% of SCC lesions. There was significantly higher expression levels of CK19 in SCC than in AK and BD (P0.05). In addition, BD lesions harboured a significantly higher number of CK19-positive cells than did AK lesions (P0.05). There were significant differences in Ki-67 labelling indices between AK and BD and between AK and SCC (P0.001), but not between BD and SCC (P0.05). Furthermore, a serial section comparison study showed that there was a minor population of cells co-expressing CK19 and Ki-67 in a subset of the tumour cells of SCC samples. The percentage of CK19+ cells significantly correlated with that of Ki67+ cells in all examined neoplastic skin lesions.These results suggest that CK19 expression may be associated with the retention of stem cell characteristics or a state that is uncommitted to terminal squamous differentiation.