Cancer of unknown primary, often called CUP, is cancer that is found after it has already spread, when doctors cannot find where it started. It accounts for about 2 to 3 percent of all cancers, and it is one of the most frightening diagnoses a person can receive, because most cancer treatment is chosen according to where the cancer began. Modern testing has changed this. Laboratory tests can now often identify the likely origin, and genetic testing can find treatable targets whatever the origin. This article explains the tests, the newest research, and integrative options.
The Tests That Can Trace the Origin
Expert pathology. Special stains on the biopsy, called immunohistochemistry, identify proteins that point to the tissue of origin, such as breast, lung, colon or prostate.
Gene expression tests. These tests compare the activity of many genes in the tumor with patterns from known cancer types to predict where the cancer most likely began.
Comprehensive DNA and RNA sequencing. Sequencing finds treatable changes in many cancers of unknown primary, such as HER2, BRAF, ALK, NTRK, FGFR2 and mismatch repair deficiency, which can be treated whatever the origin. When a biopsy is difficult, a blood test for tumor DNA can help. See our articles on tumor DNA and RNA sequencing and ctDNA liquid biopsy.
The German CUPISCO Trial
In the CUPISCO trial, led by Alwin Krämer at the German Cancer Research Center in Heidelberg and published in The Lancet in 2024, 436 people with cancer of unknown primary had comprehensive genetic testing of their tumors. After initial chemotherapy, those who switched to treatment matched to their tumor’s genetic changes went longer before the cancer grew, 6.1 months compared with 4.4 months with continued chemotherapy.1 It was the first randomized trial to show that genetic testing improves outcomes in this disease.
Research From China and Japan
China. In the Fudan CUP-001 trial at Fudan University Shanghai Cancer Center, a 90-gene expression test was used to predict each patient’s tissue of origin, and treatment was chosen for that cancer type. Compared with standard chemotherapy, this extended the time before the cancer grew to 9.6 months, from 6.6 months.2
Japan. An earlier Japanese trial of the same approach did not find a benefit,3 which shows that the results depend on the test used and the treatments available. In the Japanese NivoCUP trial, the immunotherapy drug nivolumab shrank tumors in about one in five patients with cancer of unknown primary, leading to its approval in Japan.4 Cancers with mismatch repair deficiency or a high tumor mutational burden respond especially well to immunotherapy. See our article on how immunotherapy works.
When the Pattern Points to a Likely Origin
Some patterns are treated as a known cancer, with good results. For example, women with cancer found only in the lymph nodes of the armpit are usually treated as having breast cancer, cancer in the neck lymph nodes is often treated as head and neck cancer, and well-differentiated neuroendocrine cancers are treated as neuroendocrine tumors. See our articles on stage 4 breast cancer, head and neck cancer and neuroendocrine tumors.
Integrative Research for Advanced Cancer
Because cancer of unknown primary is varied, natural treatments have not been studied in it specifically. Two have been studied in people with advanced solid tumors more broadly:
Melatonin, from Italy. In an Italian randomized trial of 250 people with metastatic solid tumors, adding melatonin to chemotherapy roughly doubled both the rate of tumor shrinkage and one-year survival and reduced side effects (Lissoni and colleagues, European Journal of Cancer, 1999). See our article on melatonin.
Mistletoe, from Germany. A German review of randomized trials found that people with cancer who received mistletoe extract alongside standard treatment reported better quality of life, including less fatigue and better sleep and appetite (Loef and Walach, BMC Complementary Medicine and Therapies, 2020). See our article on mistletoe therapy.
These are some of the natural and integrative options studied in advanced cancer, and others have promising research as well. Which may fit your situation depends on your tumor testing, your current treatment and possible drug interactions. In a consultation, Dr. Silver, MD, educates you on these options and the research behind them. Request a consultation.
How Cancer Expert MD Helps
Cancer Expert MD provides education and consultation for people with every type and stage of cancer, and specializes in Stage IV and metastatic cancer. Our guide to what to do when treatment stops working explains re-testing and the next steps, and our book, The New Reality of Cancer, covers testing and treatment across all cancers.
Frequently Asked Questions
What is cancer of unknown primary?
Cancer found after it has already spread, when the place where it started cannot be found. It accounts for about 2 to 3 percent of cancers.
Can testing find where the cancer started?
Often. Special stains on the biopsy and gene expression tests can predict the likely origin, and genetic sequencing can find treatable targets whatever the origin.
What did the CUPISCO trial show?
In this German-led trial, treatment matched to the tumor’s genetic changes kept the cancer controlled longer than continued chemotherapy, the first randomized proof that genetic testing helps in cancer of unknown primary.
Does immunotherapy work for cancer of unknown primary?
In some patients. In the Japanese NivoCUP trial, nivolumab shrank tumors in about one in five patients, and cancers with mismatch repair deficiency respond especially well.
About the author. Dr. Silver, MD, graduated from Temple University School of Medicine, trained as an interventional cardiologist, and has practiced medicine for nearly fifty years. A lymphoma survivor of about twenty-five years, he is co-author, with Dr. Lindmeier, DHSc, of The New Reality of Cancer: The Science of Recovery. Read more about Dr. Silver, MD.
Research by Dr. Lindmeier, DHSc, cancer educator and co-author of The New Reality of Cancer.
This article is for general education only and is not individual medical advice. Always consult your own doctor before making any changes to your care.
© 2026 Lovely LYF LLC. All rights reserved. This article draws on the research in The New Reality of Cancer and may not be copied, republished or distributed without written permission.
For more in-depth information on this topic and many others, get our book, The New Reality of Cancer: The Science of Recovery.
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References
- Krämer A, Bochtler T, Pauli C, et al. Molecularly guided therapy versus chemotherapy after disease control in unfavourable cancer of unknown primary (CUPISCO): an open-label, randomised, phase 2 study. The Lancet. 2024;404(10452):527–539.
- Liu X, Zhang X, Jiang S, et al. Site-specific therapy guided by a 90-gene expression assay versus empirical chemotherapy in patients with cancer of unknown primary (Fudan CUP-001): a randomised controlled trial. The Lancet Oncology. 2024.
- Hayashi H, Kurata T, Takiguchi Y, et al. Randomized phase II trial comparing site-specific treatment based on gene expression profiling with carboplatin and paclitaxel for patients with cancer of unknown primary site. Journal of Clinical Oncology. 2019;37(7):570–579.
- Tanizaki J, Yonemori K, Akiyoshi K, et al. Open-label phase II study of the efficacy of nivolumab for cancer of unknown primary (NivoCUP). Annals of Oncology. 2022;33(2):216–226.
This article is for education only. It is not medical advice and does not diagnose or treat any condition. Cancer Expert MD has no financial relationship with any laboratory, drug maker, supplement company, clinic or hospital.
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