Making an accurate diagnosis of actinic keratosis (AK) based on the histology is crucial as it can directly influence treatment decisions. However, one expert says it can sometimes be challenging for a pathologist to distinguish between AK and squamous cell carcinoma (SCC) in situ.
While the definitions of actinic keratosis, SCC in situ and invasive SCC are well-defined and agreed upon, the interpretation of the histology can be very subjective and may differ among pathologists and their individual judgement of key histologic parameters.
Therefore, it is crucial for clinicians to include clinical information regarding the lesion for correlation. This will help a pathologist arrive at an accurate diagnosis, which enables the dermatologist to prescribe the most appropriate therapy, says Travis Vandergriff, M.D., associate professor in the department of dermatology, and dermatopathologist at UT Southwestern Medical Center, Dallas.
“There is a clear consensus regarding the definitions of these lesions but then making the judgement of whether or not some of the criteria that we use to distinguish them are actually fulfilled is a lot more subjective than I think people realize,” he notes.
The main difference between SCC in situ and AK is that in SCC in situ, the full thickness of the epidermis is involved with atypical proliferation of keratinocytes; whereas, in AK, the atypia is limited to lower levels of the epidermis and not its full thickness. The critical point is making the histopathologic judgement on whether the full thickness is involved with atypia or perhaps just the lower two-thirds of the epidermis. This judgement differs among individual pathologists and, according to Dr. Vandergriff, there is some discretion that pathologists use to decide whether or not the criteria are met.
Similar to the assessment of dysplastic nevi and other melanocytic neoplasms, there is a certain amount of interpretation that is involved by the pathologist and, as such, the inter-observer agreement can often diverge. Dr. Vandergriff stresses that this is not due to a lack of education or knowledge about the criteria, but more about the subjective interpretation of the individual pathologist if the criteria are being met.