[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Skin](https://durgical.com/en/general-pathology/areas/skin/) › Actinic keratosis and squamous cell carcinoma # Actinic keratosis and squamous cell carcinoma - Lesion Rough sun spots are early, precancerous changes. Some turn into squamous cell carcinoma, the second commonest skin cancer. Updated Nov 12, 2026 ## Key points - Actinic keratosis: rough, scaly, sandpaper-like patches on sun-exposed skin; basal atypia, parakeratosis, solar elastosis; TP53 mutations. - Bowen disease: full-thickness atypia (SCC in situ); on the penis it is called erythroplasia of Queyrat. - Risk factors: UV (chief), immunosuppression after organ transplant (risk rises dramatically), HPV, arsenic, ionising radiation, chronic scars and ulcers (Marjolin ulcer), xeroderma pigmentosum. - Invasive SCC: nests of atypical squamous cells with keratin pearls invading the dermis. - Keratoacanthoma: rapidly growing crater with a keratin plug in older people; often regresses; treated as a well-differentiated SCC. - Metastasis is uncommon but higher in lips, ears, scars and immunosuppressed patients. ## What it is Actinic keratosis is keratinocyte dysplasia caused by chronic sun exposure, a precursor that may regress, persist or progress. Full-thickness dysplasia is squamous cell carcinoma in situ (Bowen disease), and invasion of the dermis is invasive squamous cell carcinoma. Cutaneous squamous carcinoma is usually curable by excision but metastasises more often than basal cell carcinoma, particularly in immunosuppressed patients. ## Structure - Actinic keratosis: atypical basal keratinocytes, budding, parakeratosis with sparing of adnexal ostia, solar elastosis in the dermis. - SCC in situ: atypia at all levels, loss of maturation, intact basement membrane. - Invasive SCC: irregular nests and strands, keratin pearls, intercellular bridges; grade by differentiation. - Keratoacanthoma: symmetric cup-shaped lesion of glassy keratinocytes around a central keratin plug. ## Step by step - UVB causes pyrimidine dimers; failure to repair them (as in xeroderma pigmentosum) increases mutations. - TP53 is mutated early; keratinocytes resist apoptosis and form clones. - UV also suppresses skin immunity by impairing Langerhans cell function. - Basal atypia (actinic keratosis) extends to full thickness (in situ carcinoma). - Further mutations (NOTCH, CDKN2A, HRAS) allow invasion through the basement membrane. ## Clinical notes - Transplant recipients develop many aggressive SCCs; HPV and immunosuppressive drugs add to UV. - Marjolin ulcer: SCC in a chronic burn scar or wound; aggressive. - Sun protection reduces actinic keratoses and SCC. ## Memory aid Actinic keratosis is the sun's rough draft; Bowen is the full text in situ; SCC is the book published into the dermis. ## Test yourself Think of the answer, then tap the question to see it. ## Which population has the greatest increase in cutaneous SCC risk? Immunosuppressed organ transplant recipients. ## What is the histologic definition of SCC in situ (Bowen disease)? Full-thickness atypia of the epidermis with an intact basement membrane. ## What is a Marjolin ulcer? Squamous cell carcinoma arising in a chronic scar, burn or non-healing ulcer. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/actinic-keratosis-and-squamous-cell-carcinoma/) [More Pathology questions →](https://durgical.com/en/practice/?f=pathology) ## Elsewhere in DurgiPedia - [Radiation and cancer: ultraviolet and ionizing](https://durgical.com/en/general-pathology/radiation-and-cancer-ultraviolet-and-ionizing/) - [Dysplasia and carcinoma in situ](https://durgical.com/en/general-pathology/dysplasia-and-carcinoma-in-situ/) - [Oncogenic viruses and H. pylori: the table to know](https://durgical.com/en/general-pathology/oncogenic-viruses-and-h-pylori-the-table-to-know/) ## Connections ## Related 5 - [Basal cell carcinoma](https://durgical.com/en/general-pathology/basal-cell-carcinoma/) - [Skin infections: the biopsy](https://durgical.com/en/general-pathology/skin-infections-the-biopsy/) - [Dysplasia and carcinoma in situ](https://durgical.com/en/general-pathology/dysplasia-and-carcinoma-in-situ/) - [Radiation and cancer: ultraviolet and ionizing](https://durgical.com/en/general-pathology/radiation-and-cancer-ultraviolet-and-ionizing/) - [Genomic instability: mismatch repair, BRCA and xeroderma pigmentosum](https://durgical.com/en/general-pathology/genomic-instability-mismatch-repair-brca-and-xeroderma-pigmentosum/) ## Related conditions 6 - [Actinic keratosis](https://durgical.com/en/conditions/actinic-keratosis/) - [Cutaneous squamous cell carcinoma](https://durgical.com/en/conditions/cutaneous-squamous-cell-carcinoma/) - [Xeroderma pigmentosum](https://durgical.com/en/conditions/xeroderma-pigmentosum/) - [HIV infection and AIDS](https://durgical.com/en/conditions/hiv-infection-and-aids/) - [Keloid and hypertrophic scar](https://durgical.com/en/conditions/keloid-and-hypertrophic-scar/) - [Burns (thermal, chemical, electrical; inhalation injury)](https://durgical.com/en/conditions/burns/) ## Microorganisms 1 - [Human papillomavirus](https://durgical.com/en/microbiology/human-papillomavirus/) [← All of general pathology](https://durgical.com/en/general-pathology/) Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [Skin Cancer Treatment (PDQ®)–Health Professional Version](https://www.cancer.gov/types/skin/hp/skin-treatment-pdq) (National Cancer Institute, 2025); [Skin Cancer](https://medlineplus.gov/skincancer.html) (MedlinePlus, US National Library of Medicine, 2025). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/general-pathology/actinic-keratosis-and-squamous-cell-carcinoma/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/actinic-keratosis-and-squamous-cell-carcinoma/