Introduction

The abscopal effect describes the phenomenon in which tumor regression occurs in a location distant from the direct target of the local therapy. This effect has been reported in numerous malignancies including lung carcinoma, melanoma, hepatocellular carcinoma, lymphoma, sarcoma, thyroid carcinoma, and renal cell carcinoma, among others [1, 2]. This phenomenon is quite rare, with only 46 reported cases in the literature between 1969 and 2014 [1]. However, its occurrence has increased with the implementation of immune checkpoint inhibitors as a synergistic effect between radiotherapy and immunotherapy occurs [2, 3]. An exact mechanism is yet to be discovered, but involves local inflammation, release of tumor antigens, and activation of T cell immune response. The abscopal effect has been reported mainly with radiotherapy but more recently with locoregional therapies as well. This report describes a case of the abscopal effect occurring after bland particle embolization of the right bronchial artery branches supplying papillary thyroid metastases to the lung.

Case report

A 74-year-old woman with a history of metastatic papillary thyroid cancer with local spread to the neck status post thyroidectomy approximately 27 years prior, two remote I-131 radioactive iodine treatments (27 and 18 years prior) and stereotactic body radiation therapy to the mediastinum and right 6th rib 5 years prior presented with progression of bilateral pulmonary nodules and small volume hemoptysis. While the I-131 scan did not demonstrate uptake, CT showed multiple bilateral pulmonary nodules and a paratracheal lymph node. The paratracheal lymph node thought to be causing dysphagia was excised and demonstrated BRAF positivity on genomic testing. Surveillance of the lung nodules with PET/CT showed increase in size, number, and metabolic activity of pulmonary nodules (Fig. 1A), however, her oncologist was hesitant to start therapy prior to embolization due to her recurrent hemoptysis. Dobrafenib and Trametinib in combination can cause serious bleeding problems and so caution was used [4–6]. Bronchoscopy localized the origin of bleeding to the right upper lobe. Right bronchial angiography was performed, demonstrating hypertrophic right bronchial arteries with diffuse hyperenhancing right lung nodules (Fig. 1B) and areas of neovascularity (Fig. 1C). Particle embolization was performed of two right bronchial arteries using 500–700-μm Embospheres (Merit Medical Systems Inc., South Jordan, UT, USA). The left bronchial arteries were not treated. On a PET/CT 10 weeks later, performed as a baseline prior to initiating systemic therapy, the patient's bilateral pulmonary nodules were significantly decreased in size, number, and metabolic activity (Fig. 1D) without interval cancer-related treatment and despite isolated treatment of the right lung. Distant metastases also displayed decreased metabolic activity on PET. The patient and her oncologist opted not to pursue additional therapy following a shared-decision making process. At follow up IR clinic visit at 3 months, the patient reported interval complete resolution of hemoptysis.

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A) Pre-procedure PET/CT demonstrating innumerable bilateral hypermetabolic pulmonary nodules. B) Right bronchial artery angiogram demonstrating innumerable enhancing right pulmonary nodules. C) Digital subtraction angiogram of the superior branch of the right bronchial artery demonstrating an enhancing lesion with neovascularity. D) Follow-up PET/CT 10 weeks post-embolization demonstrating decreased size, number and metabolic activity of diffuse pulmonary nodule and distant metastases, suggestive of abscopal effect

Citation: Imaging 16, 1; 10.1556/1647.2024.00174

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Discussion

The abscopal effect has been reported following interventional oncologic treatments including low-dose brachytherapy, cryoablation, radiofrequency ablation and trans-arterial radioembolization [3, 7, 8]. These therapies have been shown to change the tumor microenvironment, leading to cell-mediated immunity. Tumor destruction is thought to create a type of in vivo vaccine which primes the T cells to target other tumor sites in the body, thus inducing systemic anti-tumor effects [3, 8]. This response is believed to be heightened with the addition of immunotherapy. Both trans-arterial chemoembolization and bland hepatic trans-arterial embolization have been shown to change T cell populations [3], although the clinical significance is less clear. Although bland embolization has an effect on the immune response, it is not usually considered a trigger for the abscopal effect as seen in the current case, and further evaluation of the immunomodulatory effects of bland embolization is warranted.

In interpreting the results of this study, it is important to consider the potential limitations. One such limitation is the variation in the imaging modality used for assessing treatment response as the PET scans were performed using scanners at two different institutions, which could introduce variability in the measurements. While efforts were made to standardize the imaging protocols, variations in scanner characteristics may have influenced the observed differences in tumor response.

Conclusion

While the exact mechanisms underlying the abscopal effect remain to be elucidated, this case adds to the growing body of evidence supporting the role of local therapies in inducing a systemic anti-tumor response. Further investigation is warranted to explore the clinical implications and potential synergistic effects of combining bland embolization with immunotherapy in patients with metastatic cancer. Ultimately, unraveling the mechanisms underlying the abscopal effect holds promise for developing novel therapeutic strategies to improve outcomes in cancer patients.

Authors' contribution

All author's contributed to writing and review of the manuscript and approved the final version of the manuscript for submission.

Funding sources

No financial support was received for this study.

Conflict of interest

The authors have no conflict of interest to disclose.

Ethical statement

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. IRB approval was not required for this research paper as it presents a case report.

Informed consent

Informed consent was obtained from all individual participants included in the study.

Consent for publication

Consent for publication was obtained for every individual person's data included in the study.