6. Lung Neoplasms

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Ramones,Planeta Reina V.


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Lung Neoplasms

Lung cancer is the leading cancer killer in the United

States. Every year, it accounts for 30% of all cancerdeathsmore than cancers of the breast, prostate,

and ovary combined.

It is the second most frequently diagnosed cancer inthe United States, behind prostate cancer in men and

breast cancer in women.

In the annual report to the nation on the status ofcancer in 2007, it was noted that the incidence oflung cancer in men has begun to decrease, while

incidence has remained stable in women.


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most patients are diagnosed at an advanced

stage of disease, so therapy is rarely curative.

The overall 5-year survival for all patients with

lung cancer is 15%, which makes lung cancerthe most lethal of the leading four cancers.


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Epidemiology Cigarette smoking is the primary cause of lung cancer,

with smoking-related cancers accounting forapproximately 75% of all lung cancers worldwide in2007.

Two lung cancer types

1. squamous cell carcinoma2. small cell carcinoma

are extraordinarily rare in the absence of cigarettesmoking. The risk of developing lung cancer escalates

with the number of cigarettes smoked and thenumber of years of smoking, and is higher whenunfiltered cigarettes are used.


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Even after smoking cessation, however, the

risk never drops to that of people who never

smoked, regardless of the length ofabstinence. Approximately 25% of all lung

cancers worldwide and 53% of cancers in

women are not related to smoking, and themajority of these (62%) are adenocarcinomas.


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Secondhand (or passive) smoke

exposure

- has been shown to confer an excess risk

of developing lung cancer of 24% when a

nonsmoker lives with a smoker.Pre-

existing lung disease confers an increased

risk of lung cancerup to 13%for

individuals who have never smoked. This

increase is thought to be related to poor

clearance of inhaled carcinogens and/or

to the effects of chronic inflammation.


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Other causes of lung cancer include :

exposure to a number of industrial

compounds, including asbestos, arsenic,and chromium compounds. Of particularnote is the ominous combination of

asbestos exposure and cigarettesmoking, which together have amultiplicative effect on risk, as opposed

to an additive effect.


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Patients with COPD are at higher risk for lungcancer than would be predicted based on

smoking risk alone. A previous history oftuberculosis with secondary scar formationalso leads to a higher risk of primary lungcarcinoma.

Over 3000 chemicals have been identified intobacco smoke, but the main chemicalcarcinogens are polycyclic aromatichydrocarbons. Once inhaled and absorbed,

these compounds become mutagenic throughtheir activation by specific enzymes, bindingto macromolecules such as DNA and theninducing mutations.


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The lung can be conveniently viewed as two

linked components:

1. the tracheobronchial tree (or conductingairways component)

2. the alveolar spaces (or gas exchange

component).


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The tracheobronchial tree consists of

approximately 23 airway divisions to the level

of the alveoli. It includes the:1. main bronchi

2. lobar bronchi

3. segmental bronchi (to designatedbronchopulmonary segments)

4. terminal bronchioles (i.e., the smallest

airway vessels, which lack alveoli and arelined by bronchial epithelium).


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The tracheobronchial tree

is normally lined by pseudostratified ciliated

columnar cells and mucous (or goblet) cells, bothof which derive from basal cells. Ciliated cellspredominate.

Goblet cells

which release mucus, can significantly increase innumber in acute bronchial injury, such asexposure to cigarette smoke.

The normal bronchial epithelium also containsbronchial submucosal glands, which are mixedsalivary-type glands containing mucous cells,serous cells, and Kulchitsky cells.


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Kulchitsky cells

- this are neuroendocrine cells

-they also are found within the surface

epithelium.

*The bronchial submucosal glands can give

rise to salivary glandtype tumors (previously

referred to as bronchial gland tumors),

including mucoepidermoid carcinomas and

adenoid cystic carcinomas.


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The alveolar spaces or alveoli have two primarycell types,

1. type I pneumocytes

-cover 95% of the surface area of the alveolarwall but constitute only 40% of the total numberof alveolar epithelial cells. These cells are not

capable of regeneration because they have nomitotic potential.

2. type II pneumocytes

-cover only 3% of the alveolar surface but

constitute 60% of the alveolar epithelial cells. Inaddition, clusters of neuroendocrine cells areseen in the alveolar spaces.


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Preinvasive Lesions

As with epithelial tumors in other organs,

precancerous changes can be seen in therespiratory tract.

Three precancerous lesions:

1. squamous dysplasia and carcinoma in situ2. atypical adenomatous hyperplasia

3. diffuse idiopathic pulmonary

neuroendocrine cell hyperplasia.


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Note:

The termprecancerous does not mean that an

inevitable progression to invasive carcinoma

will occur, but such lesions, particularly thosewith high-grade dysplasia,do constitute a clear

marker of the potential for later development

of invasive cancer.


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Squamous Dysplasia and Carcinoma InSitu

Cigarette smoke can induce a metaplastic changeof the tracheobronchial pseudostratifiedepithelium to squamous mucosa, which is anormal response to injury.

* With the development of cellular abnormalitiesin the metaplastic squamous mucosa, squamousdysplasia evolves.

* It involves increased cell size, an increasednumber of cell layers, an increasednucleus:cytoplasm ratio, increased mitoses, andchanges in cellular polarity.


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Gradations are considered mild, moderate, or

severe.

Carcinoma in situ

- represents carcinoma still confined by the

basement membrane.

invasive squamous cell carcinoma

-Once the in situ tumor invades beyond the

basement membrane,


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Atypical Adenomatous Hyperplasia

-it is defined as a lesion


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Diffuse Idiopathic PulmonaryNeuroendocrine Cell Hyperplasia

- is a rare lesion representing a diffuseproliferation of neuroendocrine cells butwithout invasion of the basement membrane.

- It can exist as a diffuse increase in the numberof single neuroendocrine cells or as smalllesions 5.0 mm in size or that breach

the basement membrane are carcinoidtumors.


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6. Lung Neoplasms