The Use of ctDNA Testing for Surveillance and Early Detection in Solid Tumors in a Radiation Oncology Practice
Faculty and Abstracts
Purpose: Circulating tumor DNA (ctDNA) surveillance can be used as an adjunctive modality in post treatment surveillance. In this case series, we provide 4 instances (definitively treated triple-negative breast cancer (TNBC) and HPV/p16+ head and neck cancer patients) in which a radiation oncology survivorship clinic employed ctDNA surveillance, along with guidelines recommended follow-up, to facilitate earlier recurrence detection and initiation of treatment. This tool presents an opportunity to help radiation oncologists be more involved in the management of cancer recurrence.
Methodology: This study is a retrospective case series of four patients with TNBC or Head and Neck cancer receiving quarterly ctDNA surveillance post-definitive treatment. Positive results prompted further diagnostic evaluations.
Results: We present four patients in a community radiation oncology practice:
Patient 1: 63-year-old male with p16+ cT2N1M0 squamous cell carcinoma of the oropharynx, who completed chemoradiation (6/29/21), was in remission (NED) on exam and imaging until ctDNA testing (7/25/22) became positive. Subsequent investigations were unremarkable until a PET-CT on 1/5/23 showed bone metastasis, which was biopsy confirmed. Palliative radiation to L2-3 and right innominate was started alongside systemic therapy.
Patient 2: 62-year-old male with p16+ cT2N1M0 squamous cell carcinoma of the oropharynx, who completed chemoradiation (8/30/21), showed NED until ctDNA testing (7/26/22) became positive. Subsequent investigations were unremarkable but ctDNA levels continued to increase. Eventually, PET-CT (9/25/23) revealed two small avid lung metastases and a single hilar lymph node metastasis. Biopsy confirmed metastatic disease and tumor board recommended SBRT and systemic therapy.
Patient 3: 71-year-old female with cT2N0M1 Grade 3 TNBC treated with chemoradiation and bilateral mastectomy (12/8/21), post-op staging: ypT1BN1AM0. She was NED until ctDNA testing (09/2022) became positive. PET-CT (10/6/22) showed hepatic metastases. Systemic therapy was started and two months later, her ctDNA decreased and PET-CT (2/6/23) showed a good response to treatment. Unfortunately, by 05/2023 her ctDNA level started to increase and PET-CT on 5/17/23 and 7/24/23 showed disease progression.
Patient 4: 55-year-old female with cT2N2BM0 Grade 3 TNBC treated with chemoradiation and bilateral mastectomy (3/14/22), post-op staging: ypTisN2AM0. She was NED until ctDNA (08/1/22) became positive. PET-CT (9/8/22) revealed new hepatic and bone metastases. Palliative radiation was delivered to T6, T9, L1, left sacrum, and right femur on 9/23/22 and she started a new systemic therapy on 10/5/22.
Conclusions: These cases highlight ctDNA’s role in cancer surveillance in 4 asymptomatic patients, which led to earlier recurrence detection and prompt treatment. Additionally, the role of the radiation oncologist in the management of these recurrences was enhanced since they were involved in the detection and subsequent management. To further assess ctDNA’s potential, more studies focusing on different solid tumor types will be necessary.
