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How Is Carcinoma of Unknown Primary Classified?

If your doctor still cannot find the primary site of the cancer after doing a number of different tests, you may be officially diagnosed with carcinoma of unknown primary origin (CUP). A pathologist will review the biopsy samples and typically classify the cancer as one of these five most common types:

  • Squamous cell carcinoma

  • Adenocarcinoma

  • Poorly differentiated carcinoma

  • Neuroendocrine carcinoma

  • Poorly differentiated malignant neoplasm

The pathologist's classification of the cells from the biopsy will help your doctor to determine a treatment plan, even if the original site of the cancer remains unknown. 

You may need some of these additional exams:

  • Underarm lymph node evaluation

  • Groin lymph node evaluation

  • Pelvic organ evaluation

  • Chest or abdomen evaluation

  • Evaluation of other locations

  • Test for melanoma of unknown primary origin in your neck, underarms, or groin lymph nodes

Doctors will repeat a careful physical exam and maybe some of the prior tests. They will have a second pathologist look at the biopsy samples. Sometimes, as time passes, a small hidden primary tumor may become large enough to be found. This may help the doctors reclassify the CUP.