# Case Report: Histological Transformation to Atypical Carcinoid in RET Fusion-positive NSCLC Following Immune Therapy Resistance

## TL;DR

This case report describes a rare instance of lung cancer changing to atypical carcinoid after immune therapy resistance and responding to a specific drug.

## Contribution

First reported case of histological transformation to atypical carcinoid in RET fusion-positive NSCLC after immunotherapy.

## Key findings

- A patient with NSCLC developed atypical carcinoid after resistance to immune therapy.
- The patient had a RET fusion mutation and responded well to selpercatinib treatment.
- This case highlights a potential treatment option for rare mutation-associated carcinoid tumors.

## Abstract

近年来，免疫检查点抑制剂（immune checkpoint inhibitors, ICIs）已成为驱动基因阴性晚期非小细胞肺癌（non-small cell lung cancer, NSCLC）治疗的基石，然而耐药不可避免且机制尚不明确。其中，组织学类型转化是罕见的免疫耐药机制，目前仅有个案报道。本文报道了首例经一线ICIs联合化疗后组织学类型转化为不典型类癌的肺腺癌，探讨了组织类型转化在NSCLC获得性免疫耐药机制中的关键作用。此外，患者携带转染重排基因（rearranged during transfection, RET）融合突变，在发生组织类型转化后试用塞普替尼治疗取得了良好的疗效，本例为合并罕见突变的不典型类癌患者提供了可能的药物治疗选择。

Cases with histological transformation following immunotherapy