Abscopal Regression of a Lung Metastasis Induced by Microwave Ablation of Locally Recurrent Renal Cell Carcinoma

Spontaneous regression of distant metastases, known as “abscopal” effects, have been reported infrequently after percutaneous ablation. Although the exact mechanisms underlying tumor regression are unclear, potential immunomodulation after ablation may be contributory. This report describes abscopal regression of lung metastasis after microwave (MW) ablation of a local recurrence of renal cell carcinoma (RCC). University of Massachusetts institutional review board approval was not required at the participating institution for the purposes of this case report. A 77-year-old man with hypertension and atrial fibrillation presented with gross hematuria after initiating coumadin for stroke prevention. Abdominal magnetic resonance imaging demonstrated a right renal mass measuring 8.4 cm, with tumor invasion into the renal pelvis and the intrarenal portion of the renal vein, consistent with T3aN0M0 RCC. The patient underwent a robotic nephrectomy with retroperitoneal lymph node dissection. Pathology revealed T3aN0 clear-cell RCC with negative margins. Four months after surgery, computed tomography (CT) scans revealed no evidence of disease, and the patient was followed up with periodic surveillance scans. At 16 months after nephrectomy, chest CT revealed a 5-mm lung nodule in the right upper lobe (RUL), which had, in retrospect, been present 6 months prior, when it measured 3 mm. A follow-up CT scan of the abdomen/pelvis performed 20 months after nephrectomy revealed a 17-mm nodule within the surgical bed, with stability of the RUL nodule. Given the patient’s age and asymptomatic oligometastatic disease, he opted for active surveillance after a risk-benefit discussion. Two years after surgery, the RUL nodule, now 9 mm, became lobulated (Fig a–f). Positron emission tomography (PET)–CT revealed moderate 18F fluorodeoxyglucose (FDG) uptake and further growth of the nodule to 1.2 cm. The PET-CT also showed continued growth, FDG uptake, and central necrosis of the soft tissue density within the nephrectomy bed. The pulmonary nodule was biopsied 27 months after surgery without procedural adverse events, and pathology demonstrated clear-cell RCC. After multidisciplinary discussion, a decision was made to pursue a biopsy and ablation of the lesion in the nephrectomy bed first, with plans for ablating the pulmonary nodule subsequently. The surgical bed lesion was biopsied without adverse events and was confirmed to be clear-cell RCC. Under CT guidance, a 15-cm microwave probe (Emprint CA15L2; Medtronic, Minneapolis, MN) was placed into the upper portion of the lesion, which was ablated by applying 75 W for 10 minutes with ablation of the tract during retraction. After hydrodissection away from the adjacent small bowel, the lower portion of the lesion was ablated by applying 60 W for 6 minutes. Postablative CT demonstrated satisfactory result without adverse events. Surveillance scans performed 2 months after this treatment showed a slight reduction in the size of the RUL lesion; thus, the decision was made not to ablate this area as originally planned. At 8 months after nephrectomy bed ablation, a chest CT demonstrated reduction of the nodule to 9 × 5 mm2 from 9 × 11 mm2 before treatment. At 25 months after ablation, the patient continued to do well clinically. The surgical fossa lesion remained stable with treatment effect, and the lung nodule had regressed further, with only residual scar tissue seen on his most recent scan. Local therapies leading to distant effects (abscopal effects) were first described approximately 70 years ago. Percutaneous ablative techniques used in RCC include radiofrequency (RF) ablation, MW ablation, laser, and cryoablation, primarily in the context of not only treating small renal masses but also for palliative control of oligometastases, allowing clinicians to continue current treatment or offer treatment breaks for maintaining quality of life (1Morris C.S. Baerlocher M.O. Dariushnia S.R. et al.Society of Interventional Radiology position statement on the role of percutaneous ablation in renal cell carcinoma: endorsed by the Canadian Association for Interventional Radiology and the Society of Interventional Oncology.J Vasc Interv Radiol. 2020; 31: 189-194.e3Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar). Regression of distant metastasis after RF ablation has been previously reported in patients with RCC (2Rao P. Escudier B. de Baere T. Spontaneous regression of multiple pulmonary metastases after radiofrequency ablation of a single metastasis.Cardiovasc Intervent Radiol. 2011; 34: 424-430Crossref PubMed Scopus (37) Google Scholar). However, regardless of the ablation modality or disease, pulmonary metastases appear the most common site of abscopal disease regression. The off-target effects of these local treatments are believed to be primarily mediated through the activation of the host immune system primed against metastatic lesions. Postablative abscopal effect directs the regression of established disease by potential antigen priming, likely aided by cellular debris at the site of treatment. Furthermore, MW ablation likely alters the endothelial and epithelial barrier, in a manner analogous to radiotherapy ablation, allowing improved immune cell trafficking at the tumor site (3Cytlak U.M. Dyer D.P. Honeychurch J. Williams K.J. Travis M.A. Illidge T.M. Immunomodulation by radiotherapy in tumour control and normal tissue toxicity.Nat Rev Immunol. 2022; 22: 124-138Crossref PubMed Scopus (40) Google Scholar). This mechanism is distinct from the enhanced systemic antitumor immune response observed with cytoreductive nephrectomy, which is otherwise impeded by proinflammatory cytokines released by the primary tumor (4Flanigan R.C. Debulking nephrectomy in metastatic renal cancer.Clin Cancer Res. 2004; 10: 6335S-6341SCrossref PubMed Scopus (58) Google Scholar). The regression of a metastatic site from MW ablation of a local recurrence and the physiologic dependence of distant metastases on the primary tumor and mechanisms underlying abscopal responses merit further evaluation. The authors acknowledge the intellectual support of Larry Zheng, MD, and Thomas Fitzgerald, MD.