In many countries, it is standard practice to give patients with colorectal cancer metastases in the peritoneum chemotherapy before a major surgical procedure. In the Netherlands, doctors have long taken a more cautious approach. Now, the largest study ever conducted in this field shows that this caution was justified. Additional chemotherapy does not improve survival and places a heavy burden on patients.
For Ignace De Hingh, oncological surgeon at Catharina Hospital, professor at Maastricht University and principal investigator, this is the central message of the CAIRO6 study, published in The Lancet Oncology. “The assumption that more treatment is better for this patient group simply does not hold”. He notes that many international oncologists considered chemotherapy such an obvious part of treatment that a study omitting it was almost unimaginable. That makes the outcome of this study all the more significant.
Study
The study demonstrates that extra chemotherapy offers no survival benefit for this large group of patients. It is rather associated with substantial side effects. This finding also ties to a broader question in oncology. Should clinicians treat everything technically possible, or only what demonstrably adds value? The Dutch conservative approach is now supported by robust scientific evidence.
Patient care
The results are not only scientifically relevant but also important for patients. Chemotherapy is costly, physically demanding and, crucially, reduces quality of life. If a treatment has no proven effect, De Hingh argues, clinicians must reconsider whether it should be offered at all. “The fact that most patients appear not to need chemotherapy is, I think, a win for patients”.
The study also aligns with the principle of appropriate care, strongly promoted by the Dutch government. This simply means not doing everything technically possible, but doing what is meaningfully proven. De Hingh, who presented the results at the world’s largest oncology congress in Chicago and several other international conferences, even calls the study an example of this principle.
Not an end
At first glance, the study may seem ‘negative’, the investigator acknowledges. “It does not show that extra chemotherapy provides more benefit. Positive studies often attract more attention. A new treatment that does show effect is easier to promote”. Yet he sees the outcome as good news. “Patient survival after the procedure turned out better than expected. And if you can demonstrate that no additional chemotherapy is needed to achieve that, you prevent people from undergoing an unnecessarily heavy treatment”.
Controversy
“For some foreign oncologists, chemotherapy around this surgery was so self‑evident that they could hardly imagine conducting such a study. For them, it almost felt unethical”.
That is precisely why the outcome is so important. “In the Netherlands, we managed to investigate this question properly. And now we see that extra chemotherapy adds nothing for this large group, while side effects are significant. What this study shows most clearly is that the critical attitude of Dutch oncologists was not conservatism, but evidence‑based caution”.
“This does not close the topic. It rather helps us move forward”. The next step is to better predict which patients do and do not benefit from major abdominal surgery. “We are looking at a combination of factors, such as pathology, radiology, surgical reports and care outcomes”. Follow‑up studies on other treatment strategies are already underway. “We continue searching for ways to improve survival further”.
Seed
The idea for the study originated about fifteen years ago, in a conversation that made De Hingh reconsider his assumptions. “Because it was the international standard, I referred a patient for chemotherapy. But the oncologist asked, ‘Where is the evidence?’ That question planted the seed for the study”.
The research followed patients from ten hospitals, nine in the Netherlands and one in Belgium and spanned over nine years. It is the largest study worldwide in this patient group.
The study was set up and coordinated by Catharina Hospital and supported by grants from KWF and the Catharina Health Foundation. Participating hospitals included Amsterdam UMC, UMC Utrecht, Erasmus MC, Antoni van Leeuwenhoek, Radboudumc, UMCG, St. Antonius Hospital, Medisch Spectrum Twente and Ziekenhuis Oost‑Limburg (Genk).
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