Penile metastasis from a duodenal gastrointestinal stromal tumor: A rare case report

Abstract

Penile metastases are rare, and metastasis of a gastrointestinal stromal tumor (GIST) to the penis is exceedingly uncommon. An 81-year-old man with a history of duodenal GIST, initially treated with curative resection and tyrosine kinase inhibitor therapy for liver metastasis, presented with an enlarging penile mass. A biopsy confirmed penile metastasis from GIST. To relieve his symptoms, a total penectomy was performed. Molecular testing revealed a KIT exon 9 mutation and CDKN2A/B gene alterations, indicating aggressive tumor behavior and resistance to standard treatment. This case underscores the importance of recognizing atypical metastatic sites in GIST.

Highlights

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Rare case of penile metastasis from duodenal gastrointestinal stromal tumor (GIST).
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Total penectomy provided symptomatic relief but did not prevent disease progression.
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Molecular testing revealed a rare KIT exon 9 mutation and CDKN2A/B gene alterations.
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Genetic profiling stressed the aggressive nature of atypical GIST metastases.

1 Introduction

Gastrointestinal stromal tumor (GIST) is rare neoplasm of mesenchymal origin, typically arising from the stomach or small intestine. Duodenal GISTs account for less than 5 % of cases, and metastasis commonly involves the liver or peritoneum. Penile metastases are an extraordinary clinical finding, with less than 500 cases reported across all malignancies and only one involving GIST. ^, Here, we report the second known case of penile metastasis from GIST, originating from a duodenal primary tumor.

2 Case presentation

An 81-year-old man with a history of prostate cancer and lung adenocarcinoma, both in remission following radiotherapy, was diagnosed with duodenal GIST during evaluation for anemia. The tumor was surgically resected via subtotal gastrectomy with pancreas-preserving duodenectomy. Pathology confirmed a spindle-cell GIST with low mitotic activity (2/50 HPF) and KIT positivity, classified as low risk for recurrence per the Modified Fletcher criteria.

Three years postoperatively, hepatic metastases were detected, and the patient was started on imatinib (400mg daily). Despite treatment, the patient developed a progressively enlarging penile mass over the next year. MRI demonstrated a well-demarcated subcutaneous lesion on the ventral aspect of the penis ( Fig. 1 ). Biopsy revealed spindle-shaped cells consistent with GIST, confirmed by positive KIT immunostaining. The patient underwent total penectomy for symptomatic relief. Pathological evaluation confirmed penile metastasis from GIST, with tumor infiltration beneath the penile skin and displacement of the corpora cavernosa ( Fig. 2 ). Pathology of the resected penile tumor confirmed a spindle-cell GIST with high mitotic activity and KIT positivity, classified as high risk of Modified Fletcher criteria ( Fig. 3 ). Molecular testing revealed a KIT exon 9 mutation in both the primary and penile metastatic sites. However, no alteration was found in platelet-derived growth factor receptor alpha (PDGFRA) genes. A comprehensive genomic profiling test in the metastatic site revealed Cyclin-dependent kinase inhibitor (CDKN) 2A/B gene alterations were found. Despite continued systemic therapy, the disease progressed rapidly, and the patient succumbed six months later.