# Acral metastasis of colonic cancer: A case report

## TL;DR

A rare case of colorectal cancer spreading to the fingertip is reported, highlighting the importance of considering acral metastasis in cancer patients with unexplained digital lesions.

## Contribution

This case report documents an extremely rare acral metastasis of colorectal cancer to the digits, emphasizing diagnostic challenges and clinical implications.

## Key findings

- Acral metastasis of colorectal cancer to the digits is rare, occurring in 0.007–0.2% of cases.
- Immunohistochemical staining is essential to distinguish metastatic CRC from primary digital tumors.
- Digital lesions in cancer survivors should raise suspicion for acrometastasis to ensure timely diagnosis.

## Abstract

Colorectal cancer (CRC) is the third most common malignancy worldwide and accounts for 9.4% of all cancer-related deaths, making it the second leading cause of cancer mortality. Approximately 70% of patients develop metastatic disease, most commonly to the liver and lungs. Acral metastasis, particularly to the digits, is extremely rare and usually indicates advanced disease with a poor prognosis.

We report a rare case of digital acrometastasis from colorectal adenocarcinoma in a 55-year-old male. The patient presented with a painful lesion on his right index finger, characterized by discoloration, a wound cavity, and granulation tissue at the fingertip. The patient had a prior history of treated colon cancer and was receiving immunotherapy. He underwent wedge excision and nail avulsion of the affected finger. Histopathological examination confirmed metastatic adenocarcinoma with an immunohistochemical profile consistent with colorectal origin. The patient was referred to the National Center for Cancer Care and Research (NCCCR); however, no follow-up information was available, as he did not return for further evaluation.

Bone metastasis from CRC is uncommon, and acrometastasis to the digits occurs in only 0.007–0.2% of cases. The differential diagnosis of digital lesions can be challenging and should include both benign and malignant conditions. Immunohistochemical staining is crucial for diagnosis, and with metastatic CRC typically expressing cytokeratin 20 (CK20) and caudal type homeobox (CDX2), it helps distinguish it from primary digital adenocarcinomas. Clinicians should consider acrometastasis in patients with a history of CRC who present with unexplained digital lesions.

This case underscores the rare potential of CRC to metastasize to acral regions, including the distal phalanges. Clinicians should maintain a high index of suspicion for metastatic disease when evaluating digital lesions in patients with a history of malignancy, as timely diagnosis and management are essential for optimizing patient outcomes.