In a Thymic carcinoma, the tumors grow more quickly than thymomas and have a greater propensity for capsular invasion, metastases, and recurrence. They are usually advanced when diagnosed, and are often resistant to chemotherapy. Patients with thymic carcinoma have a worse survival compared with thymoma. The cells that make up the carcinoma no longer look like normal thymus cells, but cancer cells from the pathological standpoint.

Some studies have suggested a possible link with exposure to radiation to the upper chest area, but this has not been confirmed. The only known risk factors, based on case studies, are age and ethnicity.

Some types of Thymic carcinomas may be less aggressive than others, and have a more favorable prognosis.

Thymic Neuroendocrine Tumor (Thymic Carcinoids)

When a pathologist looks at cancer cells, they apply certain stains, or coloring agents, before looking at the cells under a microscope. The way the cells appear when stained tell the pathologist the type of cancer. Thymomas and thymic carcinomas are from epithelial cells that line the surface of the thymus. There are also thymic carcinoid tumors that arise from glandular endocrine-hormone producing cells that are found in small quantities in the thymus. These cells can be found almost anywhere in the body, but is largest amounts in the small intestine. Other places containing endocrine cells include the appendix, rectum, and lung.

In some very rare cases, thymus cells may be ectopic, which means in a location in which they are not normally found. The most likely place for ectopic thymus cells is in the neck near the thyroid gland as a result of abnormal migration during fetal development. During fetal development, the cells that make up the thymus migrate down to the mediastinum. In very rare cases, some of this tissue fails to migrate, forming in the neck

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Staging