External expressions of internal malignancy.

Paraneoplastic conditions are cancer-connected but are not produced as a direct effect of the tumor or metastasis. Some antedate the appearance of the internal malignancy; some run a course parallel to the tumor; some follow a pattern independent of the neoplasm. They occur in a small minority of patients with cancer and are, for the most part, of unknown cause. When an external disorder is present, it may act as a marker of hidden malignancy and thus contribute to its detection, or it may serve as an indicator of successful treatment. Many of the conditions described occur commonly without any underlying malignancy, but an unusual frequency of association with cancer makes their presence significant.