Small cell lung cancers (aka SCLC and oat cell cancer) is a malignant condition of the epithelium usually arising from the central airways and specifically arising from the eneterochromaffin or Kulchitsky cell which embryologically originates from the neural crest. They account for 15-25% of lung cancers, and thus are less common than NSCLC. There is a definite causal relationship with cigarette smoking. The age population is slightly younger than the NSCLC group (27-66yrs SCLC vs 44-61yrs in NSCLC). SCLCs grow more quickly than NSCLCs and are more likely to metastasize early. Often, they have already spread to other parts of the body when the disease is diagnosed.
Structurally the tumor tends to be central , is bulky, fast growing, and usually with early hilar and mediastinal involvement. The malignant cells are characterized by their small size (as their name implies) being <21 microns which is slightly smaller than 2-3 lymphocyte diameters. They also resemble the lymphocyte in shape and character. Most of the population of cells is round to oval in shape but spindle-or polygonal forms occur as well.
The cytoplasm is usually sparse and the nuclii show a high mitotic rate as a result of the rapid growth. The nuclii are granular characterized by a salt and pepper appearance with small or inconspicuous nucleoli. The characteristic feature of malignant cells with a high nuclear to cytoplasmic ratio is also present.
Since they are central tumors, diagnosis is sometimes attained by cytological washings.
Clinically the patient may manifest with the effects of the tumor on the on the larger airways that includes cough, hemoptysis, dyspnea, and wheezing. The central location and tendency to bulky mediastinal involvement sometimes results in SVC syndrome. Paraneoplastic syndromes are characteristic of the disease as well.
The diagnosis is suspected by the CT appearance which shows bulky disease in the hilum and mediastinum. The approach to management is based on whether the disease is “limited” which would allow single port treatment with XRT as opposed to “extensive” disease which implies it has spread beyond the chest or requires more than one XRT port. PET scanning is extremely useful in staging the disease.
Treatment invokes both XRT and chemotherapy. The tumor has a remarkable and characteristic response to chemotherapy being specifically sensitive to mitotic inhibitors. It is this characteristic unique response to chemotherapy that prompted the division and classification of lung cancers into SCLC and NSLC.
Overall median survival for SCLC is 6-10 months. Patients with limited disease have 2 year survival of 10% and for extensive disease it is only 3%. 70 % of patients have extensive disease on presentation.