## Malignancy Association in Acanthosis Nigricans **Key Point:** Gastric adenocarcinoma is the most common internal malignancy associated with acanthosis nigricans, accounting for approximately 50–70% of malignancy-associated cases. ### Frequency of Associated Malignancies | Malignancy | Frequency | Region Notes | | --- | --- | --- | | Gastric adenocarcinoma | 50–70% | Most common worldwide; higher in Asian populations | | Lung cancer | 10–15% | Second most common | | Breast cancer | 5–10% | Less frequent | | Ovarian cancer | 5–10% | Particularly in women | | Lymphoma | 3–5% | Rare association | **High-Yield:** In an Indian patient presenting with acanthosis nigricans and internal malignancy, gastric cancer should be the first consideration, especially given the higher prevalence of gastric malignancy in the Indian subcontinent. **Clinical Pearl:** Acanthosis nigricans can precede, accompany, or follow the diagnosis of malignancy. When it appears suddenly in an adult without obesity or endocrine disease, malignancy screening is mandatory. ### Pathophysiology The exact mechanism remains unclear, but insulin-like growth factor (IGF) and transforming growth factor-α (TGF-α) produced by tumour cells are thought to stimulate epidermal growth factor receptors on keratinocytes, leading to hyperkeratosis and papillomatosis. 
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