Cancer and the Immune System

The body's immune system attacks and elimi­nates not only bacteria and other foreign sub­stances but also cancer cells. A cancer cell is not a foreign cell; rather, it is a cell whose biologic function has been altered in such a way that it doesn't respond to the body's normal mecha­nisms for controlling cell growth and reproduc­tion. The abnormal cells can continue to grow, resulting in cancer.

Much of the body's protection against cancer is carried out directly by cells of the immune sys­tem rather than by antibodies circulating in the bloodstream. For example, the presence of tu­mor antigens on cancer cells can activate certain white blood cells (lymphocytes and, to a lesser degree, monocytes), which carry out an immunologic surveillance, looking for cancer cells and destroying them.

The immune system's critical role in controlling cancer cell development is exemplified by an astounding statistic: Cancer is 100 times more likely to occur in people who take drugs that sup­press the immune system (for example, because of an organ transplant or a rheumatic disease) than in people with normal immune systems. In addition, sometimes a transplanted organ has a cancer that wasn't diagnosed before the trans­plantation. The cancer may have been growing slowly or not at all in the organ donor. However, the cancer starts growing and spreading rapidly in the recipient, whose immune system is sup­pressed by drugs to protect the transplant. Typi­cally, when the immunosuppressive drugs are stopped, the transplanted organ is rejected and the transplanted cancer is destroyed as well.

Immunotherapy.

To improve the immune system's ability to find and destroy cancer, researchers have developed biologic response modifiers. These substances are used for the following functions:

· T o stimulate the body's antitumor response by increasing the number of tumor-killing cells or producing one or more chemical messengers (mediators)

· To serve directly as tumor-killing agents or chemical messengers

· To decrease the body's normal mechanisms for suppressing the immune response

· To alter tumor cells to increase their likelihood of triggering an immune response or make them more likely to be damaged by the immune system

· To improve the body's tolerance to radiation therapy or the chemicals used in chemotherapy

Interferon is the best-known and most widely used biologic response modifier. Almost all hu­man cells produce interferon naturally, but it can also be made by recombinant molecular biologic techniques. Although its mechanisms of action are not totally clear, interferon has a role in the treatment of several cancers. Excellent responses (including some cures) have occurred in about 30 percent of people with Kaposi's sarcoma, 20 per­cent of young people with chronic myelogenous leukemia, and 15 percent of people with renal cell carcinoma. In addition, interferon prolongs the expected disease-free period in people who are in remission from multiple myeloma and some forms of lymphoma.

In killer cell therapy, some of a cancer patient's own lymphocytes (a type of white blood cell) are removed from a blood sample. In the laboratory, the lymphocytes are exposed to a substance called interleukin-2 (a T-cell growth factor) to cre­ate lymphokine-activated killer cells, which are injected back into the person intravenously. These cells are more capable than the body's nat­ural cells of detecting and destroying cancer cells. Although about 25 to 50 percent of the people who have malignant melanoma or kidney cancer re­spond well to lymphokine-activated killer cell therapy, this form of therapy is still experimental.

Humoral (antibody) therapy boosts the body's production of antibodies. Substances such as extracts of weakened (attenuated) tuberculosis bacteria, which are known to boost the immune response, have been tried with some cancers. In­jecting the tuberculosis bacteria directly into a melanoma almost always causes the cancer there to recede. Occasionally, the effect extends to tu­mors that have spread to other parts of the body (metastases). Doctors have also successfully used tuberculosis bacteria to control bladder cancer that has not invaded the bladder wall.

Another experimental approach involves link­ing tumor-specific antibodies with anticancer drugs. The antibodies, which are synthesized in the laboratory and injected into a person, guide the drugs to cancer cells.

Alternatively, other antibodies created in the laboratory can adhere to both the cancer cell and a killer lymphocyte, bringing the two cells to­gether so the killer lymphocyte can destroy the cancer cell. So far, such research hasn't resulted in any widely applicable cancer therapies.

Recent research offers hope for new treat­ments. Some of them use pieces of oncogenes, which are important in cell regulation and growth.

Notes:

immunosuppressive drugs лекарственные средства, подавляющие иммунитет

the body's tolerance to radiation therapy переносимость организмом лучевой терапии

malignant melanoma (злокачественная) меланома

 

Diagnosis of Cancer

Text A. Diagnosing Cancer.

 

An evaluation of cancer begins with a history and physical examination. Together, they help a doctor assess a person's risk of cancer and decide which tests are necessary. In general, as part of a routine physical examination, a cancer-related checkup should be performed to check for can­cers of the thyroid, testes, mouth, ovaries, skin, and lymph nodes.

Screening tests try to identify cancer before it causes symptoms. If a screening test gives a pos­itive result, further tests are needed to be certain of the diagnosis. A diagnosis of cancer must al­ways be made with absolute certainty, a process that usually requires a biopsy. Determining the specific type of cancer is also absolutely essen­tial. When cancer is found, staging tests help de­termine its exact location and whether it has spread. Staging also helps doctors plan appropri­ate treatment and determine prognosis.

Since many different types of cancer exist and their treatments vary, diagnosing the presence of cancer and determining the specific type of can­cer are absolutely essential. This virtually always requires obtaining a sample of the suspected tumor for examination under a microscope. A va­riety of special tests on that sample may be re­quired to further characterize the cancer. Know­ing the type of cancer helps the doctor determine what tests to perform, because each cancer tends to follow a pattern of growth and spread.

In up to 7 percent of cancer patients, tests identify metastases before the original cancer is distinguished. Sometimes the original cancer cannot be discovered. However, doctors can usually identify the type of primary tumor by performing a biopsy of the metastasis and examining the tis­sue under a microscope. Nonetheless, identification is not always easy or certain. To what extent doctors search for a primary tumor is determined from the tissue diagnosis. In general, doctors seek the primary tumor if treating it will significantly affect survival (for example, breast cancer). If identifying the primary tumor will not change the program of therapy or the projected survival, ex­tensive testing to locate it has no value.

Notes:

evaluation of cancer критическая оценка наличия рака

appropri­ate treatment подходящее лечение

Text B. Staging Cancer.

 

When cancer is found, staging tests help doc­tors plan appropriate treatment and determine prognosis. A variety of tests are used to determine the tumor's location, its size, its growth into nearby structures, and its spread to other parts of the body. Staging is critical to determine if cure is likely. People with cancer sometimes become impatient and anxious during staging tests, wish­ing for a prompt attack on the tumor. However staging allows doctors to determine an intelligent, planned course of attack.

Staging may use scans, such as liver and bone scans, dye studies, or computed tomography (CT) or magnetic resonance imaging (MRI) to de­termine whether the cancer has spread. Medias­tinoscopy, in which the center of the chest (the mediastinum) is viewed with a fiber-optic instrument, is used to determine whether cancer, usually lung cancer, has spread to nearby lymph nodes. A bone marrow biopsy, in which tissue is taken from the center of a bone and examined under a microscope, can help determine whether a cancer has spread to the bone marrow.

Sometimes surgery may be needed to determine the cancer's stage. For example, a laparotomy (an abdominal operation) allows the surgeon to remove or treat colon cancer while determining whether the cancer has spread to nearby lymph nodes, from which it could travel to the liver. An analysis of lymph nodes removed from the armpit during a mastectomy helps determine how far breast cancer has spread and whether postsurgical therapy is needed. An operation to remove the spleen (splenectomy) helps in staging Hodgkin's disease.

Ultrasound scanning is a painless, noninvasive procedure that uses sound waves to show the structure of internal organs. It's helpful for identifying and determining the size of certain cancers, particularly of the kidneys, liver, pelvis, and prostate. Doctors also use ultrasound to guide the removal of tissue samples during a needle biopsy.

Computed tomography (CT) scanning is used (detect cancer in the brain, lungs, and abdominal organs, including the adrenal glands, lymph nodes, liver, and spleen. A lymphangiogram is a test in which dye is injected into the feet and followed with x-rays as it flows upward. The test helps identify abnormalities in the abdominal lymph nodes. Although uncommonly done since the advent of CT imaging, lymphangiograms con­tinue to have value in staging Hodgkin's disease and testicular cancer.

Magnetic resonance imaging (MRI) is an alter­native to CT scans. With this procedure, a very powerful magnetic field generates exquisitely de­tailed anatomical images. It is of particular value in detecting cancers of the brain, bone, and spinal / cord. No x-rays are involved, and MRI is extremely safe.

 

Tests for Staging Cancers

Cancer Site	Type of Biopsy Performed	Other Tests Performed
Breast	Needle or whole-lump biopsy	Mammogram 'Liver and bone scans Brain CT scan. Estrogen- and progesterone receptor testing on the biopsy sample
Gastrointestinal tract	Tissue for biopsy taken by endoscopy or with a needle (usually guided by a CT scan) through the skin for liver, pancreas, or other organs	Chest x-ray Barium x-ray Ultrasound scan CT scan Liver scan Blood tests for liver enzymes
Lung	Biopsy of the lung and possibly the sac around the lung (pleura) Mediastinoscopy	Chest x-ray CT scan Sputum cytology
Lymphatic system	Lymph node biopsy Bone marrow biopsy	Chest x-ray Blood cell counts Ultrasound scan CT scan Radioisotope scan Exploratory surgery Splenectomy
Prostate	Needle biopsy	Blood tests for acid phosphatase and prostate-specific antigen (PSA) Ultrasound scan
Testes	Testis removed for biopsy	Chest x-ray CT scan
Uterus, cervix, ovaries	Tissue for biopsy taken during exploratory surgery	Pelvic examination under anesthesia Ultrasound scan CT scan Barium enema examination

 

Notes:

ultrasound scanning ультразвуковое исследование (УЗИ)

needle biopsy биопсия тканей, произведенная при помощи специальной иглы

CT scan компьютерная томография

 

Complications of Cancer

Text A. Cancer Emergencies.

Cancers and their satellite tumors (metastases) invade and thereby alter the function of an organ or put pressure on surrounding tissues; either may result in a wide variety of symptoms and medical problems. In people with metastatic cancer, pain can result from the cancer growing inside nonexpandable bone, from pressure on nerves, or from pressure on other tissues.

Many cancers produce substances such as hormones, cytokines, and proteins that can affect the function of other tissues and organs, resulting in a variety of symptoms termed paraneoplastic syndromes. Sometimes the problems caused by cancer are so severe that they must be treated as an emergency.

Cancer emergencies include cardiac tamponade, pleural effusion, superior vena cava syn­drome, spinal cord compression, and hypercalcemic syndrome.

Cardiac tamponade is the accumulation of fluid in the baglike structure surrounding the heart (pericardium or pericardial sac), which puts pres­sure on the heart and interferes with its ability to pump blood. Fluid can accumulate when a cancer invades the pericardium and irritates it. The can­cers most likely to invade the pericardium are lung cancer, breast cancer, and lymphoma.

Cardiac tamponade occurs suddenly when so much fluid accumulates that the heart can't beat normally. Before the onset of tamponade, the per­son usually feels a vague pain or pressure in the chest that worsens upon lying down and gets bet­ter upon sitting up. Once the tamponade devel­ops, the person has severe difficulty in breathing; the neck veins swell during inhalation.

Doctors diagnose cardiac tamponade with chest x-rays, electrocardiograms, and echocardiograms. To relieve the pressure, a doctor in­serts a needle into the pericardial sac and draws the fluid into a syringe (pericardiocentesis). A sample of the fluid is examined under a micro­scope to see whether it contains cancer cells. Subsequently, the doctor cuts an opening in the pericardium (pericardial window) or strips the pericardium to prevent tamponade from recur­ring. Additional treatment depends on the type of cancer present.