Non-small Cell Lung Cancer
Histology/Pathology
Small Cell Lung Cancer (SCLC)
The SCLCs account for 20% of lung tumours (figure 1); they are usually centrally located and are relatively sensitive to cytotoxic chemotherapy.1 Clinically, they are associated with relatively rapid tumour growth and metastatic spread at an early stage.
Figure 1. The classification of lung cancer.1,2
Non-Small Cell Lung Cancer (NSCLC)
NSCLC represents a diverse group and includes squamous or epidermoid carcinoma, adenocarcinoma and large-cell carcinoma. Although the squamous subtype was predominant for most of the 20th century, its incidence has decreased over the last few decades. The large-cell carcinomas are undifferentiated tumours that cannot be considered in the SCLC category, but which lack squamous cell or glandular morphology and account for between 10% and 20% of lung tumours. The adenocarcinomas can usually, but not always, be characterised by their glandular macromorphology and production of mucin. In North America, adenocarcinomas have become the predominant form of lung cancer.1,2 This may partly be accounted for by changes in classification and pathological techniques, although geographical differences have also been observed. In Europe the squamous-cell type still predominates, but the proportion of adenocarcinoma has been increasing,2 as it has in Asia.2 To what extent these differences are due to differences in diagnosis remains unknown. Smoking history and exposure to passive smoking, occupational exposure, diet and cooking, pollution and other environmental factors may also play a role.2
The increasing incidence of adenocarcinoma has been suggested to be due partly to an increase in the incidence of one subtype; that of bronchioloalveolar-cell carcinoma (BAC). For example, Auerbach and Garfinkel1 found that the proportion of BACs in their sample had more than doubled from 9% (pre-1978) to 20% (1986–89). However, based on an analysis of the SEER database of the National Cancer Institute in the US, Read et al found that, although the incidence of BAC had increased between 1979 and 1998, BAC represented less than 4% of all NSCLC in each time period.
BACs are thought to arise from the terminal bronchioles and alveoli (although this is a point of much debate). The BAC tumour may spread as cuboidal or columnar ‘epithelium’ along the lining of the alveoli to involve a whole lobe. In some cases it may be seen as diffuse nodular lesions on radiographic examination. BAC can resemble metastases from other adenocarcinomas such as colon, breast or pancreas and the resulting difficulty in identification may hamper correct diagnosis and appropriate treatment. Early stage BAC does not appear to be invasive, is not as aggressive as other NSCLCs and has a good prognosis if spread has been contained within a single lobe or lung. However, surgery is contraindicated in bilateral presentation of BAC and may be of palliative use only in advanced stage BAC or on recurrence.3
References:
1. Carbone DP. The biology of lung cancer. Semin Oncol 1997;24(4):388–401.
2. Charloux A, Quoix E, Wolkove N, Small D, Pauli G, Kreisman H. The increasing incidence of lung adenocarcinoma: reality or artefact? A review of the epidemiology of lung adenocarcinoma. Int J Epidemiol 1997;26(1):14–23.
3. Barlesi F, Doddoli C, Thomas P, Kleisbauer JP, Giudicelli R, Fuentes P. Bilateral bronchioloalveolar lung carcinoma: is there a place for palliative pneumonectomy? Eur J Cardiothorac Surg 2001;20(6):1113–16.
