A Malignancy of Unknown Origin (MUO) is the term we use when a patient is diagnosed as having cancer but the origin of the cancer cannot be identified. When an MUO is diagnosed it can be very hard to accept that even with tests, the primary cancer cannot be found. You’ll probably be coping with difficult feelings, so it is important to get the support you need.
MUO are metastatic solid tumors (hematopoietic malignancies and lymphomas are excluded) for which the site of origin is not suggested by a thorough history, physical examination, chest radiograph, routine blood and urine studies, and thorough histologic evaluation.
