3621 - Detection of Oligo-Metastases in Oropharyngeal Carcinoma Following (Chemo)Radiation Therapy

R. Chelvarajah¹, Y. Liu¹, J. Su², A. Hosni Abdalaty¹, S. V. Bratman³, J. Cho⁴, E. Hahn¹, A. Hope⁵, J. Kim⁴, B. OSullivan¹, J. Ringash⁴, C. J. Tsai⁶, J. N. Waldron³, A. Spreafico⁷, E. Sanz Garcia³, D. Goldstein⁸, C. M. Yao⁹, S. H. Huang⁴, and A. McPartlin¹⁰; ¹Princess Margaret Cancer Centre, Toronto, ON, Canada, ²Department of Biostatistics, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada, ³Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada, ⁴Department of Radiation Oncology, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada, ⁵Department of Radiation Oncology, University Health Network, Toronto, ON, Canada, ⁶University of Toronto, Toronto, ON, Canada, ⁷Department of Medical Oncology, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada, ⁸Department of Otolaryngology-Head & Neck Surgery, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada, ⁹Department of Otolaryngology-Head and Neck Surgery, University of Toronto, Toronto, ON, Canada, ¹⁰Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada

Purpose/Objective(s): The benefit of ablative therapy for oligometastases (oligo-DM) has been reported. Early detection of oligo-DM vs polymetastases (poly-DM) may facilitate salvage treatment. This study investigates factors associated with oligo-DM detection (= 5 lesions, = 5 cm in size) vs poly-DM in oropharyngeal cancer (OPC) and subsequent disease outcomes. Materials/

Methods: All OPC patients who developed DM =3 months after definitive (chemo)radiation (c/RT) in 2006-2019 were identified from an in-house prospective system. Tumor HPV status was ascertained by p16 staining. Frequency and timing of imaging surveillance after 3 months post c/RT was at clinician’s discretion. DM detection was classified as symptomatic (DM or constitutional symptoms) vs asymptomatic. DM characteristic and outcomes were compared between oligo vs poly-DM. Multivariable analysis (MVA) was performed for OS after DM.
Results: A total of 124/1666 (7.6%) consecutive OPC patients developed DM. Despite similar DM rate in HPV-positive (HPV+, 91/1287, 7.1%) vs HPV-negative (HPV-, 33/379, 8.7%) (p=0.52) patients, longer interval from c/RT to DM was observed for HPV+ vs HPV- (median 16.8 [range 4.3-93.8] vs 8.6 [4.6-60.4], p<0.01). There was a similar proportion of oligo-DM for HPV+ vs HPV- (11 (33%) vs 35 [38%], p=0.75). Oligo-DM was significantly more frequent in asymptomatic versus symptomatic patients (62% vs 42%, p=0.049). Scan intervals were shorter in oligo-DM vs poly-DM (median 7.9 vs 12.7 months, p=0.03) (Table 1). Thoracic metastasis (includes lung and mediastinum) was the most common DM site for both HPV+ vs HPV- (77 [85%] vs 30 [91%], p=0.56). Only patients with oligo-DM received DM-directed salvage ablative therapy (41% vs 0, p<0.001). Median follow-up from DM diagnosis was 2.6 years. OS at 3 years after DM was higher for patients diagnosed with oligo-DM vs poly-DM (32% vs 5%, p<0.001), and, among the oligo-DM subset, for those who received ablative salvage therapy (63% vs 7%, p<0.001). On MVA, salvage ablative therapy (p<0.01) and HPV+ status (p<0.01) were associated with longer OS, while oligo-DM (p=0.18) and interval to DM detection (p=0.51) were not.
Conclusion: Lung is the most common DM site for both HPV+ and HPV- OPC. Despite similar DM rates, HPV+ DM tends to occur at a longer interval after primary treatment. Nearly one-third of OPC DM are oligo-DM regardless of tumor HPV status. Oligo-DM patients are more likely to present asymptomatic and detected following a shorter surveillance scan interval. Patients with oligo-DM who received salvage ablative therapy, and HPV+ patients regardless of DM volume, had a longer OS following diagnosis of DM. Prospective studies in utility of surveillance imaging to increase detection of oligo-DM in asymptomatic high risk OPC patients may help inform clinical practice. Abstract 3621 – Table 1: Scanning interval in DM detection

	Total DM (n=124)	Oligo-DM (n=47)	Poly-DM (n= 77)	P value
Imaging intervals				0.038
<= 6 months	30	17 (57)	13 (43)
6-12 months	77	12 (32)	25 (68)
>12 months	37	17 (30)	40 (70)