Lung cancer is now one of the best known and most feared of all diseases. There are good reasons for this reaction. Every year the numbers of Canadians diagnosed with lung cancer increase. However, this situation can change in the coming years -- primarily through decreasing the number of cigarette smokers.

Although other substances such as asbestos and coal tar products can cause lung cancer, at least 85% of the disease is related to smoking. The other inhaled cancer-producing substances increase the risk for the smoker. Not only does smoking contribute to lung cancer but also to other cancers (mouth, larynx, esophagus, bladder, kidney and pancreas), to cardiovascular disease, an even greater killer of Canadians, and to other chronic lung diseases such as emphysema.

Lung cancer is largely preventable, and the best protection is never smoking. For those who do smoke, quitting is the best course of action. The risk of lung cancer relates to the duration of smoking. The sooner a smoker stops smoking, the sooner the risk will cease to increase. Passive absorption of smoke (second-hand smoke) also increases the risk of lung cancer, even in non-smokers.

Today lung cancer is the leading cause of death from cancer in men and women. Therefore, it is vital that both public and professional efforts be directed at effectively controlling this "epidemic"

What is cancer?

Cancer is a disease in which abnormal cells in some organ or tissue go out of control, growing and increasing in number. Normal cells reproduce themselves throughout life, but in an orderly and controlled manner. Normal growth occurs, worn out tissues are replaced and wounds heal. When cells grow out of control and form a mass, the mass is called a tumor. Some tumors grow and enlarge only at the site where they began and these are referred to as benign tumors. Other tumors not only enlarge locally but also have the potential to invade and destroy the normal tissue around them and to spread to distant parts of the body. Such tumors are called malignant tumors, or cancer. Distant spread of a cancer occurs when malignant cells detach themselves from the original (primary) tumor, are carried to other parts of the body through the blood or lymphatic vessels and establish themselves in the new site as an independent (secondary) cancer. A tumor that has spread in this manner is said to have metastasized and the secondary tumor (or tumors) is called a metastasis (or metastases).

What is lung cancer?

Because of the different manner in which tissue cells in the same organ system may respond to varying types of exposure to cancer producing agents, several different types of cancer may be found in any organ. This is well illustrated by the primary cancers affecting the lung which are described below. The first three types arise in the lining membrane of the airway in the area most exposed to inhaled pollutants.

• Squamous cell cancer represents the largest number of lung cancers (approximately 40%-45%).
• Large cell undifferentiated cancer is found in about 5%-10% of lung cancer cases.
• Small cell cancers (small cell undifferentiated lesions) account for 15%-20% of all lung cancer. Because it spreads rapidly from its characteristically central location, surgery is rarely the best treatment. However, encouraging results have been obtained with chemotherapy with this kind of lung cancer.
• Adenocarcinoma usually arises in the outlying areas of the lung and accounts for 25%-30% of all lung cancers. The disease may occur in non­smokers.
• Bronchioloalvealar carcinoma arises in even more outlying areas and accounts for less than 5% of the total number of cases. It may also occur in non-smokers.
• Rare cancers of other types may be found, although they too represent a very small percentage (less than 5%) of the total number of cases.

Causes of lung cancer

As cigarette smoking is the major cause of lung cancer today, it is important to understand how it affects the lungs. Smoking causes lung cancer in two ways. First of all smoke inhalation damages the normal cleansing processes by which the lung protects itself from injury. The tube-like structures (bronchi) which conduct inhaled air to the lung tissue are lined with a single layer of cells on which lies a protective coating of mucus. Hair-like cilia on these cells beat in rhythmic fashion to move the mucus continually upwards from the lung, removing any inhaled particles which have been trapped in the sticky mucus. The effectiveness of this cleansing mechanism is destroyed very quickly by smoke inhalation because the cilia disappear and the lining thickens in an attempt to protect the delicate underlying tissues from damage.

When these changes have occurred, the lung can no longer keep itself clean. Consequently, cancer-producing agents in the cigarette smoke remain trapped in the mucus on the surface lining of the airway long enough to pass into the cells before these substances can be removed by coughing, the only cleansing mechanism which remains. Once within the body, these chemicals, or their products, can alter the nature of the cells slowly and progressively until cancer develops.

Cigarette smoking is therefore a cancer-producing form of pollution in the inhaled air which possesses not only the ability to destroy the cleansing mechanism, but also dangerous, cancer-producing chemicals. Other inhaled carcinogens will of course represent an additional hazard for the smoker once the effective cleansing function no longer protects the lung. However; when they are inhaled by a non-smoker who has a healthy bronchial lining, there is less risk.

The risk of lung cancer increases with the total amount of exposure. In cigarette smoking, several factors are involved in determining the actual exposure, including the duration of smoking, the number of cigarettes smoked and the depth of inhalation. Contrary to previous theories, women who share the same smoking history as men also share the same, or higher, risk.

The person at greatest risk is one who has smoked for many years (e.g., over 20 years), who has averaged more than 20 cigarettes per day and who has inhaled freely. For this person the risk may be increased by as much as 15-30 times compared to that of a non-smoker. Starting smoking early makes it possible for a person to have smoked heavily for at least 20 years by the age of 35.

The person who has smoked only pipes or cigars and never cigarettes, tends to "puff" rather than inhale freely, and therefore has less risk of developing lung cancer than a cigarette smoker, although it is an increased risk compared to a non-smoker's. It is important to realize that it doesn't do much good for cigarette smokers to switch to pipes and cigars. Unfortunately, once the habit of inhalation has been learned as a cigarette smoker, the individual who switches tends to continue inhaling when smoking either pipes or cigars. Indeed, the total smoking exposure may actually be increased by this change.

As already indicated, the interference with the lung's cleansing processes explains the peculiar significance of cigarette smoking. Other forms of inhaled pollutants, particularly repeated industrial exposures, may increase the risk for the smoker, although they can also affect the non-smoker. This effect has been noted in exposure to the following agents: asbestos, chromium, nickel coal tar products and radon (a radioactive gas).

Indeed the risk of developing lung cancer has been increased 50 times for asbestos workers who also smoke in comparison with the risk in the non-smoking general population. In comparison the risk for a non-smoking asbestos worker is only 5 times greater than the risk in the non-smoking general population. Both non-smokers and smokers must therefore avoid work where there is a risk from airborne asbestos. Under Provincial Occupational Health and Safety legislation, employers have a responsibility to provide a safe and healthy work place.

Passive Smoking

A series of studies have now shown that non-smoking wives are at increased risk of lung cancer from prolonged exposure to the smoke produced from the cigarettes of their husbands, if the husbands smoke. The greatest risk, approximately twice the normal low risk in non-smokers, comes from the exposure to husbands who smoke 20 or more cigarettes a day at home. Prolonged exposure to the smoke of others, in for example, the working environment, also increases risk, and this increase may apply not only to non-smokers, but to smokers as well. Particularly at risk are young children, as it has already been demonstrated that children exposed to the smoke of their parents have increased risk of respiratory infection and it has even been suggested that mothers of unborn children exposed to the smoke of others, have a greater frequency of low birth weight infants than mothers not so exposed. Health Canada figures estimate that every year at least 330 non-smokers die from lung cancer due to exposure to second­hand smoke.

Detection and Diagnosis

Regardless of the type of lung cancer, the complaints noted by the patient are very similar. Since the tumor is a foreign object in the airway, a repetitive cough develops in an attempt to dislodge it. This chronic cough may damage the surface of the tumor so that blood appears in the sputum. In addition, glands are also stimulated by the irritation of the smoke inhalation and produce increased amounts of mucus which must be coughed up.

At a later stage, the growing tumor may also completely obstruct an airway so that infection develops behind this obstruction, resulting in the signs and symptoms of pneumonia. Usually people with lung cancer complain of increased cough, fever, and sometimes chest pain. Because the obstruction prevents the effective clearing of secretions from the involved lung, the symptoms persist even if antibiotics bring the infection itself under control.

Whereas, in the past, persisting complaints of this type raised the spectre of tuberculosis, they now suggest lung cancer if a person is a cigarette smoker. Consequently, the development of these complaints demands investigation in the attempt to detect the cancer at the earliest possible moment.

Diagnostic Techniques

Once cancer is suspected, there are several techniques of investigation that can be pursued.

• Sputum can be collected and examined microscopically for the presence of malignant cells which have sloughed from the surface of the tumor. Adequate and careful sampling is required.
• Bronchoscopic examination of the airway is sometimes undertaken. In this examination the doctor passes a tube through the mouth or nose into the airways subdivision of each lung. When the obstructing tumor can be seen, a small piece of the tumor can be removed through the broncho­scope for examination under the microscope. Brushings and washings can also be taken from a suspect area for subsequent examination.
• Needle biopsy-When the tumor cannot be reached by the bronchoscope, and diagnosis has not already been established, under local anaesthesia a fine needle can be introduced through the chest wall directly into the tumor with x-ray guidance. A small sample is taken of the tissue and then examined microscopically.
• Mediastinoscopy-Since it is essential that the specific nature of the tumor be clearly estab­lished before deciding how best to treat it, addi­tional information can be obtained by making a short incision just above the breast bone down to the airway (trachea). A tube is passed through the incision downward alongside the airway to inspect the lymph nodes near the lungs. This procedure is called a mediastioscopy. If abnormalities are noted, biopsies can be obtained for examination.
• Computerized Axial Tomography (CAT) Scans are used to help your physician diagnose the presence and extent of any cancer in the lung. During this painless procedure, a narrow x- ray beam is directed by a computer to revolve around the chest area. Within seconds, thousands of bits of information are fed into the computer which converts the data into an image.
• And finally, if all other measures have failed to establish a working diagnosis, a small opening can be made in the chest (mini-thoracotomy) through which the tumor can be directly exam­ined and material obtained for diagnostic purposes.

Treatment

Once the diagnosis has been established, the decision regarding appropriate treat­ment must be made. It is important to remem­ber that a doctor treats the whole person and not the disease alone. This principle implies deciding what is best for each individual. Conse­quently, the same treatment is not necessarily used for all people with cancer.

Lung cancers are not all alike and patients themselves differ widely in their resistance to the development and spread of the cancer. Some cancers grow and spread rapidly and aggres­sively whereas others grow slowly, not spreading until very late in the development of the tumor. Similarly, some patients can reject spreading tumor cells and also maintain effective control of the local growth while others cannot. Therefore, the doctor decides whether the tumor is one which is best treated surgically, by radiation, by the use of drugs (chemotherapy), or by a combination of these measures.

If the tumor is localized so that surgery is advisable, about 30-35 per cent of the people who have lung cancer will be alive and well five years after a successful operation. Radiotherapy is considered a better method of controlling the primary tumor when it cannot be removed completely or when the patient's health indicates that surgery would be inadvisable.

The use of drugs, or chemotherapy, has in the past been used when there is evidence that the tumor has spread to other parts of the body. More recently, chemotherapy has been shown to be particularly helpful in the treatment of the small cell variant of lung cancer and an increase in long term survivals is now being reported following this form of treatment. However, overall, when all people with cancer of the lung are considered, it is obvious that prevention through smoking cessation is the best solution.

Future progress

Success in treating lung cancer depends on the type of tumor and the stage at which it is first diagnosed. Research is now being done into diagnostic techniques, and the early reporting of complaints such as persistent unexplained cough, blood spitting, or repetitive lower respiratory infection should also be encouraged.

However, with lung cancer, prevention holds the greatest hope for the future. It is always more exciting and rewarding to prevent disease than to treat it once it has developed. The fact that such a large proportion of lung cancer is so clearly related to cigarette smoking emphasizes the need to help those who wish to give up their habit and to encourage young people not to start. Today, only a few smokers have never tried at least once to stop. Techniques of smoking withdrawal have been studied extensively and have proven to be of value. Your doctor can help you with advice about smoking cessation.

Efforts are also being made, through education and public policies, to help young people and adults choose to be non-smokers.