# Near-complete pathologic resolution of untreated papillary thyroid cancer after pembrolizumab-induced thyroiditis

## TL;DR

A woman with untreated thyroid cancer showed near-complete tumor resolution after developing inflammation from a cancer drug used for breast cancer.

## Contribution

This case suggests immune checkpoint inhibitors may offer new treatment options for thyroid cancer patients.

## Key findings

- Pembrolizumab-induced thyroiditis led to near-complete pathologic resolution of untreated papillary thyroid cancer.
- The case highlights potential therapeutic use of ICIs for differentiated thyroid cancer.
- ICIs could serve as an alternative or additional treatment for advanced metastatic DTC.

## Abstract

Immune checkpoint inhibitors (ICIs) have revolutionized treatment for multiple cancers. However, research into the therapeutic potential of ICIs for differentiated thyroid cancer (DTC) is sparse. We present a case of a 55-year-old woman with untreated papillary thyroid cancer who received pembrolizumab as part of treatment for her breast cancer and then developed pembrolizumab-induced destructive thyroiditis, leading to near-complete pathologic resolution of her thyroid cancer. This suggests therapeutic potential to use ICIs in patients with DTCs who are not candidates for standard therapies such as surgical resection, and as an additional agent for patients with advanced metastatic DTC.