The most common tumor type associated with SIADH is a small cell undifferentiated carcinoma of the lung. Small cell undifferentiated carcinomas in other sites may also cause the disorder.
Other tumors that may cause SIADH include:
(1) squamous cell carcinoma of the cervix, nasopharynx, oral cavity, larynx or other sites
(2) non-small cell carcinomas of the lung
(3) adenocarcinoma of the prostate
Features of paraneoplastic SIADH:
(1) There is no evidence of SIADH prior to the development of the tumor (although SIADH may precede the recognition of the tumor).
(2) The patient develops clinical SIADH with serum hyponatremia and low serum osmolarity.
(3) SIADH may be mixed with other paraneoplastic syndromes.
(4) No other explanation for the SIADH is identified.
(5) Activity of the SIADH parallels disease activity, with improvement after therapy and worsening with disease progression.
(6) An exacerbation may occur following chemotherapy with the tumor lysis syndrome.
