Initial diagnosis. Two major categories of diagnostic problems are associated with the management of cancer ： obtaining the original diagnosis and correctly identifying the complications or intercurrent illnesses that may arise during the course of the disease. A tissue diagnosis, usually from the primary site, is required in order to allow the patient and physician the certainty to embark on a plan of treatment. Although for most patients with lung, breast, or colon cancer the initial diagnosis is straightforward, some patients may present with metastatic disease but with no apparent primary lesion, or the primary mass may not be easily accessible to needle biopsy. In these patients, identification of the primary lesion and its biopsy are mandatory steps in patient management. Indirect diagnostic techniques are not a substitute for a histologic or cytologic diagnosis of cancer. Rarely it may not be possible to obtain tissue for histologic diagnosis，e. g. , when there is a deep-seated brain tumor or when the patient’s general condition is so poor that the malignancy has little bearing on prognosis.

Physicians often face the diagnostic dilemma posed by the discovery of a metastatic lesion of unknown primary site. In searching for the primary, two rules apply： The clinician must consider the most common type of cancer in the given subject, taking into account age, sex, site of disease, and personal and family history, and must rule out the most treatable lesions, such as breast cancer in women and testicular cancer in young males. Special immunohistologic or electron microscopic studies may be required to rule out malignant melanoma or lymphoma. The finding of mediastinal, retroperitoneal, or lymph node involvement and high human chorionic gonadotropin or α-fetoprotein levels are indicative of germ-cell tumors. Cisplatin-based chemotherapy programs may cure such patients.

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