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Small cell lung cancer (SCLC) is most commonly associated with the syndrome of inappropriate antidiuretic hormone secretion (SIADH). This association arises because SCLC can produce ectopic ADH due to its neuroendocrine origin, leading to the retention of water and dilutional hyponatremia in patients.

The mechanism involves cancer cells that, although primarily located in the lungs, influence systemic physiology by secreting hormones typically produced by normal neuroendocrine cells. SIADH results when there is excessive levels of ADH leading to inappropriate water retention despite normal or low plasma osmolarity, disrupting the normal balance of fluids in the body.

Understanding this connection between SCLC and SIADH is crucial, as it impacts the management and treatment of patients with this type of lung cancer. In contrast, while other types of lung cancer may have various paraneoplastic syndromes, they are not as strongly linked with SIADH as SCLC.