Radiation generates an abscopal response and complete resolution of metastatic squamous cell carcinoma of the anal canal: a case report

Abstract

The abscopal effect is a rare phenomenon in the setting of radiation therapy (RT) for metastatic cancer where tumor regression occurs distant from the site of treatment. A proposed mechanism of the abscopal effect is the activation of a systemic antitumor immune response by localized RT. We report the first case, to our knowledge, of the abscopal effect in squamous carcinoma of the anal canal with metastases to pelvic lymph nodes, liver and bone. After palliative RT to the pelvis with sensitizing chemotherapy, complete response was observed not only in the primary tumor but also in bone and multiple liver metastases at 4 months after treatment, an effect that remained durable at 4-year follow-up. Understanding of the abscopal effect and the immune mechanisms associated with anal cancer may lead to new avenues of research to improve outcome for patients with this rare disease.

Keywords: Anal cancer; abscopal effect; chemotherapy; immunotherapy; liver metastasis; radiation therapy (RT).

Figure 1

FDG PET maximum intensity projection images showing (A) multiple liver metastases pre-treatment; (B) complete resolution of disease 3 years after treatment; and (C) durable disease control 4 years after treatment. The right renal calyces with excreted FDG are visible anterior to the liver.

Figure 2

Multi-parametric immunostaining images showing (A) staining of PD1-blue, CD8-red, and CD3-yellow in the tumor; and (B) in the stroma. Expression of PDL1-brown is shown in (C) the tumor; and (D) stromal macrophages. Magnification: 20×.

Figure S1

CT sequence.

Figure S2

CT images showing multiple liver metastases pre-treatment on left hand panel and resolution of liver disease on right hand panel 4 weeks after pelvic radiation therapy and chemotherapy (28). Available online: http://www.asvide.com/articles/1833