Lung Cancer Overview

Lung Cancer 

Lung cancer is the most rapidly growing disease facing the nation and the world today. Because of the increasing prevalence of this cancer, it has become a matter of public concern. Although lung and bronchus carcinoma is the 2nd leading source of new cancer cases, it is the leading cause of cancer deaths for both men and women. Therefore, the government (at least in the US…and Canada, by default…) has taken an active role in establishing smoking regulations in public places. 

Why is it the 2nd leading cancer diagnosis?

• There are more women smokers now than there were in the past.

59.4 million active smokers and 50 million former smokers are projected to be diagnosed with lung cancer.

The teenage group is a target population in the anti-smoking campaign because they easily adopt the addictive habit, and many don’t end up quitting. Even if they stop the habit, they still have a higher probability of developing cancer in the future.
 

What is the prognosis for lung cancer patients?

• Most people diagnosed with lung cancer die within that first year.
• Less than 40% of patients diagnosed with localized lung cancer survive 5 years.
• Less than 20% of patients diagnosed with regional lung cancer survive 5 years.
• And those with distant metastases have even poorer prognoses.

Lung cancer diagnosis is directly proportional to the amount the person has smoked. Smoking is calculated by pack-years (# packs/day x # years). 6 cigarettes/day is the lower limit of smoking that will not lead to an increased probability of developing lung cancer. Once the person has smoked over 10 pack-years, he/she will most likely develop lung cancer. 1 out of 13 people diagnosed with lung cancer die from it; the others die of emphysema, heart disease, or other complications. 

The most common cancer in the lung is due to metastases from other organ carcinomas, such as breast, colon, pancreas, stomach, and kidney. When diagnosing a patient, it is important to determine if the lung cancer is primary or metastatic. Getting a good history helps in making the diagnosis. For example, if the patient has a history of gastric or colon cancer, tumor metastases are commonly found in the lungs. The first clinical presentation of such cancers is usually pulmonary symptoms.  

There is variation of the prevalence of the different types of lung cancer in African American women. Notice that adenocarcinoma is the most common lung cancer, followed by squamous cell, small cell, and large cell carcinoma.
 

Lung Neoplasms

All tumors derive from a single common tumor cell. A stimulus from a carcinogen (e.g. pollutant) determines the type of carcinoma that will develop. As yet, we don’t know from which precursor cell or which carcinogenic agent produces cancer. 

Tumors are not homogeneous. Instead, there are mixtures of different types of cancers within tumors, making them heterogeneous. In the picture to the right, there are 2 tumor types within one tumor (small cell and squamous cell carcinomas). Generally, squamous cells are the origin of most lung cancers, and precancerous stages can be seen. However, adenocarcinoma doesn’t have precancerous stages – you either have it or you don’t. 

A solitary tumor usually signifies primary lung cancer. Multiple tumors usually signify metastatic lung cancer.
 

How Do You Get a Lung Tissue Biopsy?

A fiber-optic bronchoscope is comprised of a flexible tube with a light, pincers, and brush at one end. The pincer is used to take the biopsy of the lung tissue and the brush is used to brush off some cells from the tumor. It travels through the airways to take samples of lung tissue. Sometimes, it’s difficult to get a biopsy using the bronchoscope because most tumors are not in the bronchi but in the parenchyma.
 

Normal Lung Histology 

The mucociliary apparatus.

• Lines the respiratory tract
• Physical defense mechanism
• Mucous-producing glands
  • Mucous traps inhaled particulate matter
• Cilia
  • Push mucous up towards the mouth to be expelled

 Normal respiratory epithelium can progress to lung cancer due to smoking or inhalation of pollutants. These toxins damage the normal columnar epithelium, and can develop into squamous epithelium. The mucociliary apparatus is lost, so the person can’t cough up inhaled toxins.
 

Lung Cancer Classifications

There are four main histologic types of lung cancer.

• Squamous Cell Carcinoma (SCC)
  • This was the most prevalent form of lung cancer among males in the US, but adenocarcinoma has replaced it as the most common primary lung tumor.
• Adenocarcinoma
  • This is becoming the most common primary tumor arising in both men and women.
• Small Cell Lung Carcinoma (SCLC)
• Large Cell Undifferentiated Carcinoma (LCUC)
  • A variant of LCUC is Neuroendocrine Carcinoma (polypeptide hormone production).

 Lung cancer is also classified into three categories based on therapeutic treatments.

• Small Cell, which comprises <20% of total lung cancer
• Non-Small Cell, which comprises the majority of lung cancers (>80%)
  • Squamous cell carcinoma, adenocarcinoma, and large cell carcinoma are included in this category.
• Neuroendocrine Cancer of the Lung
  • Carcinoid, atypical carcinoid, and small cell carcinomas are included in here.

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