Small Cell Lung Cancer | Histologic Features of Small Cell Lung Carcinoma
What is small cell Lung cancer or Carcinoma
Like all cancers, lung cancer results from an accumulation of genetic changes that affect oncogenes and tumor suppressor genes. Small cell lung cancer is characterized by changes in several oncogenes, including amplification of the ‘myc’ family (L-myc and N-myc) and mutation of ‘raf’ gene.
L-myc amplification is associated with particularly aggressive behavior. Mutation inactivation of the tumor suppressor gene p53 and Rb are quite common in small cell lung cancer and the latter may be the first change during neoplastic transformation.
In addition all small cell lung cancer have a deletion of short arm of chromosome 3, where a cancer suppressor gene is likely to be found.
Small cell lung carcinomas are more common in men than in women and are strongly associated with cigarette smoking. They generally appear as pale, gray and centrally located masses with extension into the lung parenchyma and early involvement of hilar and mediastinal nodes.
These cancers are composed of small, dark, round-to-oval, lymphocytes like cells (albeit larger than lymphocytes) that have scant cytoplasm and hyper chromatic nuclei, among which mitosis are numerous. This is classical “oat” cell. In some cases tumor cells are spindle shaped or fusiform. Penetration of sub mucosal vessels is seen.
Small cell lung cancer is rapidly growing lesions that tends to infiltrate widely and disseminate early in their course and so are rarely respectable. They are therefore almost always treated by combined radiotherapy and chemotherapy, but even with these modalities, the two-year survival rate is only 5 to 8%; newer protocols have improved the outlook some what. The histogenesis of these neoplasms is still unclear.
Symptoms of small cell Lung Cancer
On the one hand, small cell lung cancer exhibit neuro-endocrine properties: expression of neuron specific enolase, presence of neuro-secretory granules (detected by electron microscopy), presence of neuro-filaments and is able to secrete polypeptide hormones which include calcitonin, gastrin-releasing peptide, ACTH and chromogranin A.
On the other hand these neoplasms may contain areas of squamous cell and adeno-carcinomatous differentiation, suggesting that the cells of origin are the same as those that give rise to all other histological variants.
Morphology: Bronchogenic Carcinoma in the various histologic categories share several features.
- They arise in lung epithelium of major bronchi, usually close to the hilus of the lung.
- All patterns are associated with cigarette smoking; the strongest association is with squamous cell and small cell lung cancer.
- All are aggressive, locally invasive, widely metastasizing neoplasms with a propensity for spread to liver, adrenals, brain and bones, although almost every organ in the body can be affected.
- Small cell lung cancer has the capacity to synthesize bioactive products, producing paraneoplastic syndrome.
These tumors being small mucosal lesions usually firm and gray-white, that may follow one of several patterns of growth. They may form intra-luminal masses; they may invade the bronchial mucosa, infiltrating longitudinally in the peribronchial connective tissue; or they may from large bulky masses pushing into adjacent lung parenchyma.
Some large masses undergo cavitations due to central necrosis or develop focal areas of hemorrhage.
Finally, these tumors may extend to the pleura, invade the pleural cavity and chest wall and spread to adjacent intra-thoracic structures. More distant spread can occur via lymphatic or the hematogenous route.
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