LUNG CANCER-PART III

     Types of lung cancer

Lung cancer is caused by the uncontrolled growth (proliferation) of abnormal cells inside the lung. There are two main forms of the disease, non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) (Barzi and Pennell, 2010).
SCLC constitutes approximately 16% of all primary lung cancers, accounting for more than 35,000 cases per year (Jemal et al., 2009).  NSCLC is the most common form of the disease, accounting for approximately 85% of all cases.  NSCLC can be further divided into adenocarcinoma, squamous cell carcinoma and large cell carcinoma. This different NSCLC types are present in different parts of the lung as shown in the figure below. SCLC is distinguished from NSCLC by its rapid growth rate, early dissemination to regional lymph nodes and distant sites, and its sensitivity to chemotherapy and radiotherapy (Masters et al., 2005). SCLC is almost exclusively caused by smoking. Two-thirds of SCLC patients present with extensive stage disease (ES-SCLC) due to a tendency to metastasize early to distant sites, including the brain, bones, liver, and adrenals (Ettinger and Johnson, 2005).

SCLC showed the smallest values for nuclear size (mean core score of 1.18) and DNA content (DNA index mean of 2.08c) being highly significantly different from adenocarcinoma (1.95/3.10c), large cell lung carcinoma (2.00/3.26c) and squamous cell carcinoma (2.20/3.42c).  In NSCLC in general and adenocarcinoma in particular, the core size variability correlated significantly with grading and survival (Petersen, 2009).

 

The prevalence of these different lung cancer types varied with sex and socio demographic variables. In the recent period, the percentage of patients with adenocarcinoma had increased significantly to 43.2% from 25.2% while that of large cell carcinoma had decreased to 3.3% from 11.9%. The percentages of patients with squamous cell carcinoma and SCLC remained stable. In the period, 1967—1976, squamous cell carcinoma was the commonest cell type in men and in smokers while adenocarcinoma was the commonest cell type in women and in never smokers. In the period, 1991—1999, adenocarcinoma was the commonest cell type in both men and women as well as in smokers and never smokers (Liam et al., 2006).

 

A retrospective study done on clinical and histopathologic data of 4,439 patients with lung carcinoma in The University of Texas Medical Branch in Galveston between January 1980 and December 2003 indicates that Adenocarcinoma has become the most frequent histologic type in men and women (36.8% and 46.5%, respectively), followed by squamous cell carcinoma (31.6% and 25.4%, respectively). The incidence of large cell (undifferentiated) carcinoma in men and women was 18.0% and 9.9%, respectively. The incidence of small cell carcinoma in men and women was 13.7% and 18.3%, respectively (Wahbah et al., 2007).

Another recent retrospective study reviewed the clinical records of 321 patients with a pathological diagnosis of advanced, non-curative stage IIIB or IV NSCLC, in Jordan between 2007 and 2009 and supports the above studies. It indicates that the most common histology was adenocarcinoma (181, 56.4%), while squamous cell carcinoma and large cell carcinoma accounted for 31% and 6.2%, respectively. Most patients were smokers at time of diagnosis (78.2%) (Abbasi and Badheeb, 2011).