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Unusual Cancers of Childhood (PDQ®): Treatment - Patient Information [NCI] - Other Rare Unusual Cancers of Childhood


Tests are done to find where the primary cancer began and to get information about where the cancer has spread. When tests are able to find the primary cancer, the cancer is no longer a cancer of unknown primary and treatment is based on the type of primary cancer.

Because the place where the cancer started is not known, many different tests and procedures may be needed to find out what type of cancer it is. If tests show there may be cancer, a biopsy is done. A biopsy is the removal of cells or tissues so they can be viewed under a microscope by a pathologist. The pathologist views the tissue under a microscope to look for cancer cells and to find out the type of cancer. The type of biopsy that is done depends on the part of the body being tested for cancer. One of the following types of biopsies may be used:

  • Excisional biopsy: The removal of an entire lump of tissue.
  • Incisional biopsy: The removal of part of a lump or a sample of tissue.
  • Core biopsy: The removal of tissue using a wide needle.
  • Fine-needle aspiration (FNA) biopsy: The removal tissue or fluid using a thin needle.

When the type of cancer cells or tissue removed is different from the type of cancer cells expected to be found, a diagnosis of cancer of unknown primary may be made. The cells in the body have a certain look that depends on the type of tissue they come from. For example, a sample of cancer tissue taken from the breast is expected to be made up of breast cells. However, if the sample of tissue is a different type of cell (not made up of breast cells), it is likely that the cells have spread to the breast from another part of the body.

Adenocarcinomas, melanomas, and embryonal tumors are common tumor types that appear and it is not known where the cancer first formed. Embryonal tumors such as rhabdomyosarcomas and neuroblastomas are most common in children.

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