CK20/CK7 double-negative merkel cell carcinoma arising within a previously photodynamic-therapy-treated actinic keratosis field: a case report
5 affiliations
- 1Department of Pathology, Tianjin Fifth Central Hospital
- 2Department of Surgery, Binhai New Area Hospital of Traditional Chinese Medicine
- 3Department of Dermatology Tianjin Fifth Central Hospital
- 4Department of General Surgery, Tianjin Fifth Central Hospital
- 5Tianjin Key Laboratory of Development and Diseases in Premature Infants, Tianjin Fifth Central Hospital
Abstract
Background: Photodynamic therapy (PDT) is a first-line treatment for actinic keratosis (AK), particularly in elderly patients. Merkel cell carcinoma (MCC) is a highly aggressive primary cutaneous neuroendocrine malignancy associated with UV exposure and immunosuppression. In skin with severe UV-induced field cancerization, it remains unclear whether PDT might activate occult highly aggressive tumors. Herein, we report an 89-year-old female who developed a CK20/CK7 double-negative MCC at the original AK site within a short period after successful PDT for AK and basal cell carcinoma (BCC), aiming to explore whether the association between PDT and subsequent MCC represents mere coincidence or a potential risk.
Case presentation: An 89-year-old female presented with a one-year history of an ulcer on the left nasal ala and an eight-month history of an erythematous patch on the left temporal region. Biopsy confirmed BCC on the left nasal ala and AK on the left temporal region, both treated with PDT (20% ALA under occlusion for 3 hours, 630 nm red light, 80–100 J/cm², three sessions). At the 3-month follow-up, both lesions had healed well. Eight months later, a firm, pale-red nodule developed at the original AK site. Histology revealed small round blue cells in the dermis; immunohistochemistry showed dot-like AE1/AE3 positivity, CD56 and NSE positivity, a Ki-67 index of approximately 75%, and negativity for CK20/CK7 and other markers. The diagnosis was primary cutaneous MCC (T2N0M0, Stage IIA) with positive surgical margins. Given advanced age and anatomical constraints, pembrolizumab was administered for 24 cycles without immune-related adverse events. Post-treatment biopsy showed no viable tumor cells. At the last follow-up in July 2026, the patient remained recurrence-free with a disease-free interval of approximately 12 months.
Conclusions: This report describes a case of CK20/CK7 double-negative primary cutaneous MCC. The temporal and spatial proximity between MCC and PDT suggests a possible causal association; however, pre-existing subclinical MCC before PDT or a coincidental second primary tumor in the context of field cancerization cannot be excluded. This report does not undermine the established role of PDT in AK management, but it emphasizes the need for individualized risk assessment and long-term surveillance in elderly patients with extensive field cancerization.
Related
- Canadian Expert Consensus Recommendations on the Use of Photodynamic Therapy in Actinic Keratosis
- From Molecular Alterations to Risk Prediction: Biomarkers of Actinic Keratosis Progression to Cutaneous Squamous Cell Carcinoma.
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BibTeX
@article{liu2026ck20ck7,
title = {{CK20/CK7 double-negative merkel cell carcinoma arising within a previously photodynamic-therapy-treated actinic keratosis field: a case report}},
author = {Min Liu and Xitao Wang and Xiaofang Ping and Chunyan Zhang},
journal = {Frontiers in Oncology},
year = {2026},
month = nov,
doi = {10.3389/fonc.2026.1946644},
url = {https://www.frontiersin.org/articles/10.3389/fonc.2026.1946644/full},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - CK20/CK7 double-negative merkel cell carcinoma arising within a previously photodynamic-therapy-treated actinic keratosis field: a case report
AU - Min Liu
AU - Xitao Wang
AU - Xiaofang Ping
AU - Chunyan Zhang
PY - 2026
DA - 2026/11/04
JO - Frontiers in Oncology
DO - 10.3389/fonc.2026.1946644
UR - https://www.frontiersin.org/articles/10.3389/fonc.2026.1946644/full
AB - Background: Photodynamic therapy (PDT) is a first-line treatment for actinic keratosis (AK), particularly in elderly patients. Merkel cell carcinoma (MCC) is a highly aggressive primary cutaneous neuroendocrine malignancy associated with UV exposure and immunosuppression. In skin with severe UV-induced field cancerization, it remains unclear whether PDT might activate occult highly aggressive tumors. Herein, we report an 89-year-old female who developed a CK20/CK7 double-negative MCC at the original AK site within a short period after successful PDT for AK and basal cell carcinoma (BCC), aiming to explore whether the association between PDT and subsequent MCC represents mere coincidence or a potential risk. Case presentation: An 89-year-old female presented with a one-year history of an ulcer on the left nasal ala and an eight-month history of an erythematous patch on the left temporal region. Biopsy confirmed BCC on the left nasal ala and AK on the left temporal region, both treated with PDT (20% ALA under occlusion for 3 hours, 630 nm red light, 80–100 J/cm², three sessions). At the 3-month follow-up, both lesions had healed well. Eight months later, a firm, pale-red nodule developed at the original AK site. Histology revealed small round blue cells in the dermis; immunohistochemistry showed dot-like AE1/AE3 positivity, CD56 and NSE positivity, a Ki-67 index of approximately 75%, and negativity for CK20/CK7 and other markers. The diagnosis was primary cutaneous MCC (T2N0M0, Stage IIA) with positive surgical margins. Given advanced age and anatomical constraints, pembrolizumab was administered for 24 cycles without immune-related adverse events. Post-treatment biopsy showed no viable tumor cells. At the last follow-up in July 2026, the patient remained recurrence-free with a disease-free interval of approximately 12 months. Conclusions: This report describes a case of CK20/CK7 double-negative primary cutaneous MCC. The temporal and spatial proximity between MCC and PDT suggests a possible causal association; however, pre-existing subclinical MCC before PDT or a coincidental second primary tumor in the context of field cancerization cannot be excluded. This report does not undermine the established role of PDT in AK management, but it emphasizes the need for individualized risk assessment and long-term surveillance in elderly patients with extensive field cancerization.
SN - 2234-943X
ER -