Circulating Biomarkers in Patients With Anal Cancer Treated With Induction Chemotherapy

Anal cancer is a rare malignancy with approximately 200 new cases in Denmark per year, and the standard treatment is chemoradiotherapy (CRT). The treatment is centralised at three oncological departments at Aarhus University Hospital, Herlev Hospital and Vejle Hospital. The majority of anal cancers are squamous cell carcinomas (SCCA) and are strongly associated with human papilloma virus (HPV) which can be detected in tumour tissue in more than 80% of cases. Patients with large tumours, tumours invading nearby organs and/or local lymph node metastases could be treated with induction chemotherapy (ICT) in cases where downsizing prior definitive treatment is needed. Selected patients with metastatic (M1) SCCA could also be treated with ICT with the purpose of making definitive treatment possible.

HPV, cell-free DNA, circulating tumour DNA and immune related markers:

HPV is a virus group consisting of more than 130 subtypes, of which a minor part is categorised as oncogenic types. The most common HPV subtypes found in SCCA is HPV-16 and -18, but the total landscape of HPV subtype distribution in SCCA is sparsely investigated. Small fragments of cell-free DNA (cfDNA) can be detected in the circulation with elevated levels in cancer patients, but also in other circumstances. Aberrant methylation of DNA occurs in almost all malignant tumours and is shed into the circulation. The level of tumour specific methylated DNA (meth-ctDNA) can be analysed by modern PCR technology. It seems to hold biological information, which holds promise of clinical utility. The literature has focused on colorectal cancer and meth-ctDNA has been introduced as a prognostic marker. The possible importance in anal cancer has not been elucidated which is one the aims of the present protocol. With a simple blood test (so called "liquid biopsy"), it is possibility to characterise both the level of total cfDNA and meth-ctDNA. HPV associated anal cancer has a viral sequence integrated into the genome of the cancer cells. In HPV associated anal cancer meth-ctDNA is shredded to the blood stream, and can be measured as HPV tumour cell DNA (plasma HPV or pHPV). The observational and translation part of the DACG Plan-A study have shown that levels of pre-treatment pHPV are higher in large tumours compared to small and higher in node positive disease compared to node negative which is in agreement with results on advanced anal cancer where pHPV levels were correlated to tumour burden. The Plan-A study have also shown that pHPV is eliminated during CRT in case of response to treatment.

Immunotherapy has changed the treatment of several malignant tumours, especially malignant melanoma. The checkpoint inhibitors block PD/PD-L1 interaction, which elicits immune response to the malignant tumour. The treatment also seems to have effect in anal cancer. The literature is sparse, but a number of studies are ongoing. It is therefore well motivated to analyse one of the central stakeholders in the immune response. The level of PD-L1 in serum holds potential as a prognostic marker in anal cancer.

Perspective: