# Spontaneous Regression of Metastatic Colorectal Cancer Following Discontinuation of an Interleukin-6 Receptor Inhibitor: A Case Report

## TL;DR

A patient with advanced colorectal cancer and liver metastasis experienced complete tumor regression after stopping an IL-6 receptor inhibitor, suggesting a link between immune reactivation and cancer regression.

## Contribution

This case report presents a rare instance of spontaneous regression of metastatic colorectal cancer following tocilizumab discontinuation.

## Key findings

- Discontinuation of tocilizumab led to complete pathological regression of both primary and metastatic tumors.
- Histopathology confirmed no viable tumor cells in the resected colon and liver.
- The patient remained recurrence-free for two years post-surgery.

## Abstract

Spontaneous cancer regression is exceptionally rare, particularly in colorectal cancer. Tumor regression has been reported in some patients with autoimmune diseases or organ transplants, after cessation of immunosuppressive therapy; however, its underlying mechanisms remain unclear. We report a rare case of Stage IVA transverse colon cancer with synchronous liver metastasis that showed complete pathological regression in both sites after discontinuation of tocilizumab, an interleukin-6 receptor inhibitor.

A 79-year-old woman with a history of rheumatoid arthritis and interstitial pneumonia was treated with iguratimod, methotrexate, prednisolone, and tocilizumab. PET-CT images revealed an accumulation of fluorodeoxyglucose in the transverse colon and liver. Colonoscopy and biopsy findings confirmed a poorly differentiated adenocarcinoma in the transverse colon; liver biopsy findings confirmed metastatic disease. In preparation for surgery, and because the rheumatoid arthritis activity was stable, tocilizumab was discontinued. Three months after tocilizumab discontinuation, laparoscopic partial colectomy with lymph node dissection was performed. Histopathologic examination of the resected colon showed no viable tumor cells. Subsequently, laparoscopic partial hepatectomy of segments 2 and 3 revealed no viable tumor cells as well. The patient remained recurrence-free at the 2-year follow-up.

The findings of this case suggest that tocilizumab discontinuation may have reactivated antitumor immune responses, resulting in spontaneous regression of both the primary colorectal cancer and liver metastasis. Notably, prior to regression, both masses were histologically confirmed as malignant lesions. This observation provides valuable clinical insight into the relationship between interleukin-6 receptor blockade, immune modulation, and tumor dynamics.