Endocrine Abstracts

Introduction: Adrenocortical carcinoma (ACC) is rare, with an incidence of 0.5-2 cases per million. Although generally aggressive, prognosis is highly variable and difficult to predict. Unlike other malignancies, there are no biomarkers routinely available for use in patients with ACC to help guide management. Circulating cell free tumour derived DNA (ctDNA), the proportion of circulating cell free DNA (cfDNA) originating from tumour cells, is a liquid biopsy that is quickly gaining favour as a clinically useful and superior biomarker in oncology but is only in the early stages of being investigated in ACC.

Aims: To identify and track ctDNA in a 60 year old male patient with metastatic ACC using a precision, patient specific approach.

Materials and Methods: Blood samples were collected at 5 time points over 25 months and separated into plasma and leucocytes. Paired whole exome sequencing (WES) was performed on leucocyte extracted DNA and DNA extracted from formalin fixed paraffin embedded ACC tissue. The 2 sequences were then compared to identify tumour specific somatic mutations. These mutations were used in the design of a bespoke Ampliseq™ HD ctDNA assay. cfDNA was extracted from plasma and the bespoke assay used to detect ctDNA through targeted next generation sequencing.

Results: This patient had a 14.5 cm left adrenal mass with lymph node metastases at presentation. WES identified 83 tumour specific somatic mutations including a TP53 mutation. 22 of these mutations (including TP53) were chosen as targets for inclusion in the Ampliseq™ HD ctDNA panel assay. Pre-adrenalectomy, 9/22 variants were detected on ctDNA analysis with variant allele frequencies (VAF) of up to 1.16%. Post-operatively, ctDNA was initially undetectable. He was commenced on mitotane however imaging later demonstrated disease progression. ctDNA analysis at this point detected 3/22 variants with VAF up to 2.72%. He received radiotherapy for bone metastases and subsequent chemotherapy following which ctDNA was not detectable on samples 4 and 5. The TP53 mutation was not detectable at any time point.

Discussion: We have demonstrated that ctDNA can be detected and tracked in a patient with ACC, with ctDNA dynamics mirroring progression and response. Targeting multiple, personalised variants is methodologically key to successful ctDNA detection. Only targeting mutations common in ACC, for example in TP53, runs the risk of missing other variants present in ctDNA. Further development is required in assay design to improve sensitivity however ctDNA is a hopeful future biomarker for patients with ACC.