the danger of wanting to overdetect cancer

The announcement was accompanied, two months later, by the technical report that evaluates extending this program, which currently includes all Spaniards between 50 and 69 years old, up to the aforementioned 74.

Although the report’s conclusion is positive, it does not avoid the main problems posed by this type of evidence, which In the middle of the last century they were considered the great promise against cancer and the passage of decades has lowered the spirit until they are demarcated only for very specific people and cancers.

“Cancer screening is carrying out tests to try to diagnose tumors before they give symptoms, when there is still no way to detect them in the clinic,” he explains. Isabel Echavarriascientific secretary of the Spanish Society of Medical Oncology (SEOM) and oncologist at the Gregorio Marañón University Hospital (Madrid).

“They have to have a technique that diagnoses them early, that is sensitive enough and that is not aggressive, because we are doing it to a healthy population,” he emphasizes.

[El miedo de los hombres a las colonoscopias lastra la detección de nuevos casos de cáncer en España]

“If the technique has a lot of risk, it may not outweigh the benefits in these people.” Furthermore, diagnosing for the sake of diagnosing is useless: “You have to be able to change the course of the disease” with early treatment.

In Spain there are three cancer screenings aimed at broad population groups. Breast and colorectal cancer tests have several similar characteristics: they are performed on the population between 50 and 69 years old (only women, in the case of the breast) with an examination every two years.

In the case of breast cancer, the test of choice is mammography. Although uncomfortable for women, in recent times it has improved both in its duration, which is increasingly shorter, and in the potential danger that radiation doses could pose.

Although, by itself, the radiation from the set of mammograms that a woman undergoes throughout her life does not reach the dangerous threshold, specialists had to consider its use if the person had been subjected to other techniques.

However, newer mammograms emit less radiation than older ones, so this danger is reduced.

The first screening

This screening was the first to be considered. In the mid-20th century, several studies began to evaluate its effectiveness, but it was not until the end of the 1980s that the first solid conclusions were reached.

They were from a study carried out in Malmo, Sweden, which followed 42,000 women over 12 years. In total, 588 cancers were diagnosed in the group that underwent mammograms and 447 in the group that did not.

This apparent success was overshadowed by the fact that this early detection had not provided much of an advantage: 63 women died in the first group and 66 in the second..

In 2002, a meta-analysis of several studies carried out in Sweden concluded that mammograms had caused a reduction of up to 30% in mortality from breast cancer, but only in women aged 55 to 70 years.

On the other hand, despite being a test with a well-established benefit-risk balance, it does not prevent a small percentage of false positives: tumors that, if not detected, would not have generated symptoms in the patient.

[El fracaso de España en la prevención del cáncer de colon: “Es el más frecuente y no se percibe el riesgo”]

But, instead of continuing with her life as if nothing had happened, she is subjected to invasive interventions, from biopsies (removal of tumor tissue) to surgical interventions and pharmacological or radiological treatments.

A review published in 2009 in The BMJ concluded that, for every death prevented with mammograms, there were about 10 women overdiagnosed.

“The problem with false positives is that they lead to many tests being performed, which generally begin with a biopsy,” explains Isabel Echavarría. “This biopsy has its discomforts depending on the area in which it is, it can even be dangerous: an unnecessary lung biopsy can carry a risk, prostate biopsies also represent a significant discomfort for patients.”

Colon cancer

The case of colorectal cancer is similar: despite having established a positive benefit-risk balance, it is not free of complications.

It is based on the detection of occult blood in feces. If the test is positive, a colonoscopy must be performed: a probe that runs through the intestine until it reaches the polyps suspected of evolving into cancer.

The Health technical report explains that there are two types of tests to detect blood in feces: one reduces mortality from colorectal cancer by 12% but not in the age groups between 70 and 80 yearsand in patients from 60 to 69 it only did so in men.

Regarding the second, the report indicates that it reduces cancer mortality up to age 69, although the quality of this scientific evidence is low.

The big problem with this screening is, however, colonoscopy, an invasive test that many people are reluctant to take. The technical document estimates 17.5 complications due to bleeding and 5.7 intestinal perforations per 10,000 procedures.

[Los médicos alertan del aumento del cáncer de colon en menores de 50: “Es una pandemia oculta”]

These are low rates but we must remember that it is a test that is done on a healthy population. In Spain there are about 12 million people between 50 and 69 years old. Only a minority of those who do a stool blood test will test positive but, as the head of the Medical Oncology Service at the Reina Sofía University Hospital in Córdoba, Enrique Aranda, recalled in a report in EL ESPAÑOL, around 95% of Those who undergo colonoscopy do not develop the disease but are exposed to the risk of the intervention.

The last major study on colorectal cancer screening showed an 18% risk reduction of developing the tumor, preventing one case in every 455. However, in absolute terms, the risk of developing it in people who were screened was 0.98% and, in those who were not, 1.2%.

The question now is: Is it worth a large investment to avoid 0.2% of cancers? The report from the group of experts estimates that expanding colorectal cancer screening to Spaniards between 70 and 74 years old would entail an annual cost of more than 10 million euros during the first five years. And that’s if only 36% of the target population participates in it.

Cervix cancer

The third of the approved screenings in Spain is that of cervical cancer. It is aimed at women between 25 and 65 years of age and consists of a cytology or smear of the cervix every three years (up to 34 years of age) and the determination of the human papillomavirus – responsible for practically all cases. of this cancer—from the age of 35.

In this case there is a special circumstance. The HPV vaccine has shown high efficacy in preventing cervical cancer. Its introduction is recent and now is when vaccinated women are reaching the age of screening, which has led to delays in testing.

For example, in Italy it has been decided to delay the start of screening in vaccinated people at the age of 30, also replacing cytology with the HPV detection test (cytology is maintained in unvaccinated people).

[Así han caído las muertes por cáncer en España en 30 años: un 25% en hombres y un 20% en mujeres]

These three screenings are the most established. However, the European Union’s anti-cancer strategy includes three more: lung, prostate and stomach cancer (by detecting the bacteria H. pylori).

Perhaps the most controversial of all of them is prostate cancer. It is based on the prostate-specific antigen or PSA test, which measures the concentration of this molecule in the blood.

Like fecal occult blood, it is a minimally invasive test. However, “The data are very controversial regarding whether or not it benefits“, laments the SEOM spokesperson, Isabel Echavarría. “There are studies that say that it does improve survival but others do not see any benefit and, in addition, it entails unnecessary biopsies and surgeries because many times tumors are diagnosed that are not going to give any problems. throughout life.”

There are studies that place the overdiagnosis of prostate cancer with this test at 60% and, furthermore, this can cause damage such as urinary incontinence without obtaining any benefit.

The European Union’s cancer plan recommends screening for prostate cancer in men up to 70 years of age using PSA determination and MRI scans as a follow-up.

In the United States, the recommendation is to avoid it in men over 70 years of age., while the decision to do so in individuals between 55 and 69 must be made at the individual level. However, this recommendation is under review and it should not be long before it is updated.

Lung, the next frontier

The test that perhaps has the most signs of becoming a reality soon is that of lung cancer. In Spain, the SEOM and the Spanish Society of Pulmonology and Thoracic Surgery have the Cassandra project underway, which studies the feasibility of looking for signs of lung cancer in heavy smokers and ex-smokers.

“We have recent data that says it does increase survival,” explains Echavarría. “What we have to see is whether it is cost-effective to do so.”

The big problem with lung cancer is that it is usually detected in advanced stages. Screening would partially solve this problem, but it involves expensive tests, such as a low-dose CT scan, which requires a large device that not all hospitals have.

In addition, it remains to determine which people should be invited. How many cigarettes does a person have to have consumed to be considered a heavy smoker? The consensus is closer to one pack a day for 20 years, but it is possible that individuals who have smoked less also have a high risk of developing cancer.

An analysis of 18 clinical trials on different types of screening published last year in JAMA Internal Medicine concluded that screening, in general, could reduce cancer-specific mortality but failed to increase longevity if the harms outweighed the benefits.

[Qué es el cribado de cáncer de pulmón y por qué ningún país en Europa lo implanta aún: las claves]

Curiously, this analysis ‘blessed’ the determination of PSA and the tomography for lung cancer, as they were associated with greater longevity, although with certain uncertainties.

Balance is difficult to achieve. Oncologists see screening as a powerful tool, although with its limits. The important thing for them is to be able to maximize the benefit of a person who will develop cancer by treating them as soon as possible.

From the point of view of health management, on the other hand, we seek to achieve a balance between the benefit achieved, the harm generated and, very importantly, the cost: the money dedicated to detecting cancer in a healthy population is money. that is not invested in other health fields.

As Josep Maria Borràs, coordinator of the national strategy against cancer, explained to this medium, “I do not agree with my epidemiology colleagues, who observe it as if they were watching traffic. In general mortality, it is possible that screening has a modest benefit. But the aim is to benefit the patient. It is about improving the prognosis, not mortality.