Screening and early diagnosis of cancer
Mikhail Davydov: using only one diagnostic method, it is impossible to reliably determine cancer
On the eve of the World Cancer Day, which is celebrated on February 4, Director of the Research Institute of Clinical Oncology of the Federal State Budgetary Institution "N.N.Blokhin RSC" of the Ministry of Health of Russia, Russian scientist, oncologist surgeon, corresponding member of the Russian Academy of Sciences Mikhail Davydov told TASS about modern diagnostic methods that reliably help to detect cancer at an early stage, about the effectiveness of tests for cancer markers and fluorography, as well as why it is so important to conduct a comprehensive examination.
– What diagnostic methods significantly reduce cancer mortality?
– It is possible to achieve a reduction in cancer mortality with the help of screening – a set of diagnostic measures that allow detecting a tumor at an early stage when there are no symptoms of the disease yet.
– What diagnostic methods significantly reduce cancer mortality?
– It is possible to achieve a reduction in cancer mortality with the help of screening – a set of diagnostic measures that allow detecting a tumor at an early stage when there are no symptoms of the disease yet.
It is necessary to distinguish screening from early diagnosis. Early diagnosis is the detection of the disease in people who themselves sought medical help after they had complaints and symptoms of the disease.
Cancer screening programs should be carried out taking into account their expediency for those forms of cancer that are an important health problem in a country or region due to the high morbidity and mortality from them.
Cancer screening should be massive, inexpensive, with high specificity, sensitivity, positive and negative predictive value. Only the fact of obtaining evidence of a reduction in mortality due to screening precedes its widespread implementation.
At the moment, the effectiveness of mass screening has been proven only for breast cancer, cervical cancer and colorectal cancer. Since the introduction of the low-dose computed tomography method into clinical practice, studies have been conducted to study the effectiveness of lung cancer screening.
According to the data provided by Professor of the Department of Oncology and Hematology of the RUDN, oncologist of the "SM-Clinic", Doctor of Medical Sciences Alexander Seryakov:
mammography reduces breast cancer mortality in women over 50 by an average of 30%;
liquid cytology reduces mortality from cervical cancer by an average of 80%;
a study on hidden blood in feces reduces mortality from colon or rectal cancer by an average of 15%.
– Do cancer marker tests help to detect cancer at an early stage?
– Many patients have confidence that tumor cells secrete certain substances that have been circulating in the blood since the onset of a malignant neoplasm, and it is enough to periodically take a blood test for cancer markers to make sure that there is no cancer. In fact, the use of cancer markers for reliable detection of cancer has not shown its effectiveness in any of the studies, which indicates that cancer markers cannot be recommended for the primary diagnosis of oncological diseases. The values of cancer markers do not always correlate with the disease.
In diagnostics, two main criteria are used by which any study is evaluated – sensitivity and specificity. Markers can be highly sensitive, but at the same time low-specific. This means that their increase may be caused not by oncological diseases, but by completely different reasons. Thus, the marker of ovarian cancer CA 125 can be increased not only in tumors or inflammatory diseases of the ovaries, but, for example, in liver disorders, inflammatory diseases of the cervix, etc. Often, cancer-embryonic antigen (REA) increases in liver disorders. Thus, the values of cancer markers depend on a number of processes, including inflammatory ones, that can occur in the human body.
Cancer markers are mainly used to monitor the course of the disease and evaluate the effectiveness of the drug treatment of malignant diseases.
– Is it possible to detect lung cancer at an early stage using fluorography?
– Does fluorography show lung cancer – many people are asking this question. This diagnostic technique has been used for many decades and with its help it is possible to identify various structural changes in the lung tissue. However, a reliable determination of oncological disease is impossible when using only one diagnostic method.
In the 80s of the XX century, fluorography was widely used as a screening method in the diagnosis of lung cancer. However, the results of several large randomized controlled trials (when participants are randomly divided into two groups: experimental, which is testing a new drug or technique, and control, which uses standard techniques or placebo. – Approx. TASS) showed that this type of diagnosis in combination with cytological examination of sputum proved ineffective and did not lead to a decrease in mortality from lung cancer.
– Perhaps there are other diagnostic methods for this type of cancer?
– Currently, a new diagnostic technique is widely implemented – low-dose spiral computed tomography. It is characterized by high sensitivity, which significantly increases the probability of detecting even small (2-3 mm) tumor formations in the lung, which, in turn, has a positive effect on the results of treatment of patients.
However, it is necessary to note the low specificity of the method. Here is an example of two major studies. In the first case, spiral computed tomography was performed in 817 men, of whom 353 (43%) had nodular formations in the lungs, but with a clarifying diagnosis, cancer was detected in only six (1.7%) patients.
In the second, as a result of a spiral computed tomography examination of 1,520 people, 775 (51%) had nodular formations of various sizes in their lungs, of which only 15 (1.9%) were malignant.
– Do those who do not smoke need to be checked?
– According to statistics available today, 85% of lung cancer patients are smokers. Thus, it can be stated that the main risk group for lung cancer is people who consume tobacco products.
Even passive smokers are 1.5–2 times more likely to get lung cancer compared to non-smokers. But this does not exclude the need for people who do not consume cigarettes to be examined for lung cancer.
– How effective is ultrasound as a method of cancer diagnosis?
– Ultrasound diagnostics allows you to study tissues and organs for the timely detection of tumors, foreign bodies, inflammatory processes, cysts and other structural disorders. This technique is accessible and simple, there are no contraindications to it. It can probably be described as the simplest and fastest in the early diagnosis of cancer.
The role of ultrasound is to quickly assess suspicious changes, sometimes with 100 percent accuracy. Recently, experience has been accumulated that expands the boundaries of ultrasound capabilities, for example, in the diagnosis of bowel and stomach cancer. Many modern ultrasound scanners are equipped with such a function as elastography. This technology allows you to evaluate the structure of a suspicious site and makes the study more accurate.
The diagnosis of abdominal cancer using ultrasound can be very accurate. Ultrasound examination of the liver helps to diagnose both primary tumors, such as hepatic cell carcinoma, cholangiocarcinoma (malignant tumor of the bile ducts), and metastatic lesions. Ultrasound of the gallbladder often reveals polyps that have the potential for malignancy and require observation. Ultrasound provides quite extensive opportunities in the diagnosis of thyroid cancer, as well as for monitoring the nature of changes in enlarged lymph nodes of the cervical-supraclavicular region.
But just like any diagnostic technique, ultrasound cannot be used independently in the diagnosis of oncological diseases. Examination of cancer patients must necessarily include a set of diagnostic techniques with morphological confirmation of the diagnosis (for example, a biopsy) and an assessment of the prevalence of the tumor process.
– Are there special ways to diagnose stomach, liver, skin cancer and leukemia? What diagnostic methods help to identify these types of cancer?
– It would probably be correct to say that for each oncopathology there are certain, the most sensitive and specific diagnostic techniques that allow detecting a malignant tumor. For example, for stomach cancer, the most accurate method for detecting a cancerous tumor is the technique of endoscopic examination – gastroscopy. For liver cancer – ultrasound, magnetic resonance imaging, skin cancer – visual examination and ultrasound.
Laboratory tests are considered to be the main methods in the detection of leukemia. An extended blood test is able to immediately determine the increased content of leukocytes and reduced platelets and erythrocytes, which indicates the presence of oncopathology. After the suspicion of chronic, acute lymphoblastic or myeloid leukemia is detected, a number of additional necessary studies are prescribed to clarify the diagnosis.
All of the above methods make it possible to identify the primary tumor in the organs under study. However, as I noted earlier, oncology is a systemic disease, and only a comprehensive instrumental examination with morphological confirmation of the detected changes allows to establish an accurate diagnosis and assess the prevalence of the disease. Only such an approach can guarantee success in the treatment of malignant tumors and give a chance for a long-term cure.
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06.02.2017