The importance of the clock in cancer diagnosis

It is revealed that the results of cancer tests may vary depending on what time of the day they are performed. The biological mechanism we call the circadian rhythm shows that it is effective in the initiation and development of cancer.

What time of day you do certain tasks can affect the result you get. For example, a study conducted in Israeli courts found that even in cases involving nearly the same crime in content, decisions made later in the day were more brutal than those made in the morning: around 70% of inmates in the early mornings received parole, while late in the day about 70% of inmates were granted parole. Less than 10% of those whose verdicts were released were evacuated. The reason for this is thought to be because people get tired as a result of the decisions they make throughout the day, known as “decision fatigue”, and their decisions in the following hours are more irrational and inconsistent. Likewise, the rates of maternal death in cesarean delivery decisions taken towards 5 pm in the USA are higher than earlier and later hours of the day; because physicians and/or nurses, whose day shift will be over, are more open to making mistakes during those hours.

A new study shows that the results of cancer tests may also depend on what time of day the test is done (and even the fight against cancer may be directly related to the time of day). But in this case, the cause is not human error. The reason is a biological mechanism we call “circadian rhythm” that regulates our sleep cycle and hormonal processes during the day.

circadian rhythm

Normally, the circadian rhythm is a biological cycle that causes our cellular functions to change throughout the day. For example, many biological parameters such as the way and amount of genes in your cells are read during the day, the qualities of your defense system, the rate of cell renewal are constantly changing, and these changes often follow a cycle that coincides with daylight. This means that your cell activity also worsens during sleep-disturbing events, such as “jet lag,” or due to long-term insomnia. So much so that even the risk of cancer increases in people whose circadian rhythm is impaired beyond a certain level! Studies show that the circadian rhythm is effective both in the onset of cancer and in cancer development and metastasis (spread of the cancer throughout the body).

Among these, metastasis is particularly important because the main factor that causes the death of cancer patients is the spread of cancerous cells to more than one point of the body (metastasis). This is where the circadian rhythm becomes important, because studies show that the rate at which tumor cells enter the bloodstream varies depending on the hour of the day. However, how much mixing occurs at which time depends on the type of cancer: For example, the risk of metastasis for breast cancer is highest at night, while the metastasis of cancers such as prostate and multiple myeloma peaks at other times of the day.


This may guide the strategy for when we should hit cancer with chemotherapy and immunotherapy. In the new article published, experts advocate a method called “chronotherapy”: Chronotherapy is the general name of treatment methods that care about the time when drugs and immune therapies are given to the body. Think of it this way: If you have a headache, it doesn’t matter when you take the pain reliever. You take the medicine, after a short time the headache goes away. But when it comes to cancer, exactly when and in what dose we give these drugs, which can have extremely severe side effects, is of paramount importance – and chronotherapy aims to maximize the benefit of this timing.

Indeed, clinical studies have shown that treatments based on chronotherapy can reduce the severe side effects that cancer drugs can cause. For example, survival rates among patients with melanoma who took immunotherapy drugs before 4:30 PM were up to 2 times higher than those who took these drugs after 4:30 PM. As I said, this time and timing strategy is different for each cancer type, and not only the time of day, but also details such as the patient’s gender and genetic background can affect this strategy.

Observing the circadian rhythm in cancer treatment can play a critical role not only in the therapy part but also in the diagnosis of cancer. For example, cancerous cells can produce different proteins at different stages of the day, and some of these proteins are used as biomarkers in cancer tests; in other words, the presence of those proteins can help determine that you have cancer in your body. Therefore, one of the effective ways to minimize false positives or false negatives can be to run tests when these proteins are most produced.

It’s really exciting that something as simple as the circadian rhythm can affect so many elements in biology. However, considering that complex systems are formed by the repetition and overlapping of very simple rules, it is not surprising that facts as fundamental as the circadian rhythm are at the center of biological processes. Understanding the mechanisms of these processes will play an important role in forever defeating the diseases and problems associated with those processes. Therefore, we must continue to support active research in these fields.

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