Cancer has many meanings. For geographers, it is the tropic of the Northern Hemisphere. For astrologers, it is a sign of the zodiac. According to statisticians, it is the leading cause of death. For the financiers it is the hope of a jackpot. For the doctor, cancer is a frequent disease that preferentially affects the middle-aged or even elderly man.
The diagnosis of cancer (www.clo2.nl: and it's limitations)
The diagnosis is often fortuitous. Cancer does not hurt; it is the palpation of a lump in the breast or prostate. Cancer can cause symptoms if it grows and compresses an organ. If the tumor blocks circulation, there will be downstream edema. When pancreatic cancer compresses the bile ducts, the patient will be jaundiced. The stools will be clear and the urine foamy. Invasion of the pleura covering the lung means that the patient will have difficulty breathing. A brain tumor can cause seizures or neurological deficit. When cancer erodes a blood vessel, there will be bleeding. For example, stomach cancers cause the patient to vomit blood and lung cancers to spit it out. A weight loss of several kilograms or a night fever signifies a diffuse and therefore advanced disease.
The clinician makes his diagnosis by examining the patient. He finds a poorly defined mass in the shape of a crab (crab = cancer in Greek). The tumor emits dendrites, which invade the surrounding tissue and make surgery difficult. The benign tumor is usually well delimited and easy to remove. On one side there is healthy tissue on the other side the benign tumor. So, the surgeon will pass a finger and easily remove the benign tumor. On the contrary, the malignant tumor (also called cancer) is poorly defined. To completely excise it, the surgeon may have to go far away from the invading dendrites.
The second clinical sign of cancer is hardness. The clinician palpates the cancerous tumor, which is hard as bone. With a simple examination, the doctor will understand the cancerous nature of the tumor. The physicist will say the tumor is under pressure.
A third sign of cancer is when the tumor bleeds easily. Blood vessels drain blood to the tumor, which bleeds at the slightest touch.
The clinician continues his physical examination for metastases. These are distant tumors emitted by the primary tumor, which are carried out by lymph and blood and will colonize the downstream territories. For example, prostate cancer spread to the lymph nodes and the bones. Melanoma of the eye spreads to the liver.
Faced with a poorly demarcated, bloody hard mass, the clinician knows he is dealing with a malignant tumor. When clinical examination is impossible, the physician performs a radiological examination. This confirms the presence of a star-shaped mass. The malignant tumor compresses the surrounding tissues that it invades with its dendrites. The search for metastases needs a radiological examination of the primary tumor. The radiological examination has its limits. It is not possible to detect tumors of less than a cubic centimeter. The detection limit is of the order of one gram of tumor around one billion cells. The radiologist frequently underestimates tumor involvement because he cannot see small lesions.
The diagnosis of cancer, even when it is obvious to the physician, has to be confirmed by the pathologist. The surgeon either removes part of the tumor (biopsy) or the entire cancerous mass. After extraction, a pathologist examines the tumor under a microscope. He will confirm the diagnosis by detecting the dendrites, which lacerate healthy tissues by invading them. It will also rule on the aggressiveness of the tumor. A low-grade tumor looks like normal cells. It will be less aggressive than an undifferentiated, high-grade tumor that has lost all sign of its original site. It is nearly 10% of cancers where the pathologist no longer finds a point in common between the cancer and the organ that gave rise to this cancer. The tumor is completely undifferentiated and has a poor prognosis.
Often the diagnosis of cancer is not obvious. There are no dendrites and the cells do not multiply at high speed. The pathologist will confirm his suspicion by analysis of the tumor genome. These tumors are borderline malignant. In situ tumors that have not yet invaded the surrounding tissues remain confined to the epithelium. They are called «cancer» but the prognosis once surgically removed is excellent. A large proportion of the breast cancers detected by screening are in situ lesions. Radiologists have reviewed X-rays of screening mammographies. Some early lesions could easily be missed. Between 14% and 50% develop into invasive lesions ten years later.
Erbas, B., Provenzano, E., Armes, J., Gertig, D. (2006). The natural history of ductal carcinoma in situ of the breast: a review. Breast cancer research and treatment, 97(2), 135-144.
We have all experienced the tragedy of Covid-19. One of the discussions focused on the very notion of “patients”. At the beginning of the epidemic, the “patients” were limited to the hospitalized men and women treated for Covid-19, then symptomatic patients and finally asymptomatic cases detected by PCR. The world of cancer suffers from the same vagueness. One cannot mix in the same study: an indolent in situ cancer and an aggressive cancer that kills within a year.