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Pathology of Actinic Keratosis

"May transform into Squamous Cell Carcinoma if left untreated"

Dr Sampurna Roy MD         


Dermatopathology Quiz Case 138

Diagnosis: Actinic Keratosis





Syn: Solar Keratosis.

Actinic keratoses are common skin lesions that appear after long-term exposure to ultraviolet radiation. 

This lesion presents as multiple scaly erythematous  patches or cutaneous horns on sun-exposed areas in middle aged and elderly patients.

They are commonly found on sites of sun-exposed skin such as the face, balding scalp, and back of the hand.

Actinic keratosis may transform into squamous cell carcinoma if left untreated.

Similar lesion on the lip is known as actinic cheilitis.

The clinical variants include

-Hyperplastic form which is commonly found on the hands.

-Spreading pigmented form which is usually found on the face.


Microscopic features:

-  Focal parakeratosis with loss of underlying granular layer.

-  Loss of orderly arrangement of the epidermis .

-  Large atypical keratinocytes are present in the epidermis.

This may vary from mild to severe.

In bowenoid type actinic keratosis there is full thickness squamous atypia.

-  Irregular bud like extension may be present in the papillary dermis.

This does not extend to the reticular dermis.

-  The dysplastic changes are not present in the adnexal epithelium.

-  Epidermolytic, pagetoid or pseudoglandular patterns may be noted.

-  In the dermis there is prominent actinic elastosis and variable chronic inflammatory cell infiltrate.

-  Hypertrophic variant is characterized by psoriasiform hyperplasia, orthokeratosis with alternating parakeratosis, mild dysplasia confined to the basal cell layer.

-  Pigmented variant displays melanin pigment in the keratinocytes and melanophages.

-  Lichenoid actinic keratosis is characterized by band like chronic inflammatory cell infiltrate, apoptotic keratinocytes, vacuolar degeneration of the basal cell layer together with parakeratosis of stratum corneum and enlarged and atypical keratinocytes.


Differential diagnosis includes superficial squamous cell carcinoma:

The following features favour squamous cell carcinoma

-  Presence of atypical keratinocytes in the reticular dermis.
-  Independent nests of keratinocyte.

Pathologists should ask for step sections in small biopsies suspected of actinic keratosis to  rule out any invasive component.

The presence of certain clinical features, such as large size, ulceration, or bleeding, suggests an increased risk of disease progression.

The risk is also increased by evidence of extensive solar damage, advanced age, and immunosuppression.

Early diagnosis and consideration for treatment are indicated to clear actinically damaged sites and diminish the risk of invasive squamous cell carcinoma.


Further reading:

Lumican as a novel marker for differential diagnosis of Bowen disease and actinic keratosis.

Key differences identified between actinic keratosis and cutaneous squamous cell carcinoma by transcriptome profiling.

Aldehyde dehydrogenase 1 expression in basal cell carcinoma, actinic keratosis and Bowen's disease.

Key differences identified between actinic keratosis and cutaneous squamous cell carcinoma by transcriptome profiling.

Dermal changes in superficial basal cell carcinoma, melanoma in situ and actinic keratosis and their implications.

Diagnostic cellular abnormalities in neoplastic and non-neoplastic lesions of the epidermis: a morphological and statistical study.

Actinic keratosis: review of the literature and new patents.

Pigmented solar (actinic) keratosis: an underrecognized collision lesion.

Assessment of cell proliferation in benign, premalignant and malignant skin lesions.

Basal cell carcinoma mistaken for actinic keratosis.

Differences in biopsy techniques of actinic keratoses by plastic surgeons and dermatologists: a histologically controlled pilot study.



Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)






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