Dear Editor, Bowen's disease, especially in genital and nail lesions and bowenoid papulosis, is recognized as human papillomavirus (HPV)-associated precancerous lesions. 1 While the association between actinic keratosis (AK) and HPV has been rarely reported, some of the beta and gamma HPV types have been reported to increase the risk of squamous cell carcinoma. 2 The aim of this study is to examine whether or not HPV is present in AK using polymerase chain reaction (PCR) and immunohistochemistry.A total of 31 tissue specimens obtained from 30 Japanese patients were examined in this study. Biopsy or surgical specimens were randomly collected from 2006 to 2016. The mean age of patients was 77 years, ranging 56-98. Among 31 AK specimens, 23 were obtained from the face, three from the ear, and one specimen from the neck, finger and forearm, respectively. Formalin-fixed, paraffin-embedded samples were cut into 10-lm sections and DNA was extracted. PCR was performed using L1C1/L1C2 and CPI/CPIIS consensus primers. 1 The amplified PCR products were electrophoresed on 2% agarose gel and the PCR products were sequenced with an automated sequencer. All assays included positive and negative controls. Immunohistochemistry was performed using sections (5-lm thick) which were deparaffinized and rehydrated through a graded series of ethanol. Sections were autoclaved in 5 mmol/L citrate buffer for 10 min at 121°C for antigen retrieval.Human papillomavirus was not detected with the L1C1/ L1C2 primer pair; however, a single band was detected in one specimen using the CPI/CPIIS primer pair (Fig. 1a). With direct sequencing, HPV type 144 was confirmed. Immunohistochemically, the HPV-positive cells were detected in the epidermis adjacent to AK (Fig. 1b), where homogenous cytoplasmic inclusion bodies were observed by hematoxylin-eosin staining (Fig. 1c). All other specimens were negative in immunohistochemistry.In the present study, we examined 31 AK specimens in order to detect HPV by PCR and found that only one specimen was positive for HPV DNA. This low detection rate is contradictory compared with previous studies that reported those of 37% 3 and 77%. 3,4 Differences in conditions of samples, such as formalin-fixed or frozen samples, race and primers may account for the discrepancy in the positive rate between previous studies and ours. HPV type 144 is a gamma virus similar to HPV types 4, 60 and 65 that are typical types of pigmented viral warts. Homogenous intracytoplasmic inclusion bodies, which are characteristic of pigmented viral warts, 5 were seen in the epidermis adjacent to AK in one specimen. We consider (a) (b) (c) Figure 1. Detection of human papillomavirus (HPV) DNA and b-globin using different consensus primer pairs and the histopathology of the HPV type 144-positive tissue. (a) HPV DNA amplification via polymerase chain reaction using CPI/ CPIIS and L1C1/L1C2 primer pairs. b-Globin DNA was amplified using PCO3/PCO4 primers. The first and last lanes indicate HPV type 16 and distilled water which are used as a positiv...