Histology of Small Cell Lung Cancer

Cancer is a complicated disease.  Lung cancer is no exception; it can be caused by four types of malignant cells.  The large majority of lung cancer cases have tumors composed of one of three subtypes of cell: squamous cells, adenocarcinoma, and large cells.  Within these categories are several specific types of cells.  The fourth cell type is very different from these forms of cancer: that is the cell associated with small cell lung cancer (SCLC).

What is the Small Cell in SCLC?

Small cell lung cancer accounts for about 15% of all lung cancer cases.  The small cell in the name is also called an oat cell, because it looks something like an oat grain in its shape and flatness.  Oat cells have very little cytoplasm in them – the gel-like material that contains a cell’s components except for its nucleus.  In normal cells most of the cellular activity occurs within the cytoplasm.  In oat cells there is almost none of this material; under the microscope an oat cell looks like it’s almost all nucleus.   These cells multiply rapidly, giving small cell lung cancer its lethal characteristics of rapid growth and rapid dispersal throughout the body.

Mixed Small Cell Lung Cancer

The two subtypes of SCLC are the oat cell cancer, consisting solely of the small cells, and mixed SCLC which is a form of lung cancer with both oat cells and one or more of the larger more common lung cancer cells.  The treatment of mixed small cell lung cancer uses the same tools as treatment of oat cell lung cancer: chemotherapy and radiation are almost always the preferred modalities.  Surgery rarely enters into the picture.

However the medications used in chemotherapy are going to be dictated by the type(s) of cancer cells which are found in addition to the oat cells.  Squamous cells respond to one type of chemotherapy drug; adenocarcinoma cells to another.  Squamous cells line the walls of the bronchi, the tubes that connect the lungs to the trachea and the location where almost all small cell lung cancers begin.  Adenocarcinoma develops from cells found in such locations as the mucus glands.  These are the two most common non-small cell cancer cell types.

Behavior of Small Cell Lung Cancer

SCLC is lethal in part because it tends to spread to other locations in the body relatively early in the course of the disease.  This early metastatic behavior is the reason that over two thirds of all small cell lung cancer cases diagnosed are in the “extended” stage, the term for advanced SCLC.  This spreading activity often occurs before real symptoms develop.  Surgery is rarely considered as a treatment option because the disease is almost never diagnosed in its early, localized stage.

Generally SCLC will form a large tumor at its point of origin and spread into the lymph system where it makes its way to distant areas of the body.  But one of the positive elements of this form of lung cancer is that it is drastically responsive to chemotherapy and radiation.  The initial manifestation of SCLC can be treated effectively with radiation and chemotherapy; however relapse occurs in the large majority of cases.

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