Most cases of cancer-related hypercalcemia are caused by tumor cells, which secrete substances that mimic or enhance the effect of parathyroid hormone. Parathyroid hormone has several functions, all leading to the release of calcium from bone into the bloodstream at a rate that exceeds the kidney's ability to excrete the excess. The primary treatment is adequate hydration, both orally and intravenously, to lower calcium levels. While hypercalcemia can usually be reversed with prompt and adequate therapy, it is associated with poor life expectancy in patients with cancer. Effusion, or abnormal fluid accumulation, may also occur in patients with cancer, particularly if the disease is in the advanced stages.
Effusion results when the balance between secretion and reabsorption is altered.
Malignant pleural effusion is debilitating and life threatening because the increased pleural fluid adversely affects respiratory function. If the underlying cancer is treatable, therapy is aimed at the primary malignancy, rather than the effusion. Spinal cord compression, which occurs when the tumor extends into the epidural space of the spinal cord. Superior vena cava syndrome, which occurs when the blood flow to the heart through the superior vena cava is reduced because of a malignancy or other causes. Syndrome of inappropriate antidiuretic hormone secretion, which occurs when a tumor decreases cardiac output, leading to increased antidiuretic hormone secretion, water retention and other problems.