br Incidence of thymic carcinoma

Incidence of thymic carcinoma The first report on a large number of cases (n = 60) with thymic carcinoma was published in 1991 by Suster and Rosai. In 2003, Kondo and Monden reported the largest series, consisting of 227 cases collected from 115 institutions in Japan. Reports of more than 20 cases of thymic carcinoma from a single institution are rare. According to the literature, the incidence of thymic carcinoma is only 0.06% of all thymic neoplasms. We have retrospectively reviewed reports on several large series on thymic carcinoma and the results are summarized in Table 1. We found that the incidence of thymic carcinoma might have geographic differences. Confirmation of such differences requires additional investigation of this relatively rare cancer. We retrospectively reviewed our experience in treating 207 patients with thymic epithelial tumors from June 1988 to November 2009. Some 37% of these patients had thymic carcinoma. We are still investigating the reason for such a high incidence of thymic carcinoma in the southwest part of Taiwan.
Signs and symptoms of thymic carcinoma Thymic carcinoma occurs most frequently in adults between 30 and 60 years of age. In some cases, thymic carcinoma is found incidentally on routine chest X-rays (20% in our series). Once a patient has symptoms, which are usually atypical chest symptoms due to mediastinal rora or invasion (53% in our series), the cancer is already at an advanced stage. Because of the anterior mediastinal location and high invasiveness, the superior vena cava syndrome is not rare. A paraneoplastic syndrome has also been reported for patients with thymic carcinoma, but is rare. Pure red cell aplasia or hyper- or hypoglobulinemia occurs primarily in thymoma rather than in thymic carcinoma. Myasthenia gravis is commonly found in patients with thymoma, but rarely occurs in patients with thymic carcinoma unless there is a concomitant thymoma component. We previously described one patient with thymic carcinoid combined with myasthenia gravis. Cushing syndrome and multiple endocrine neoplasia type I have also been reported in patients with thymic carcinoid. Pan et al reported that thymoma has a higher incidence of associated malignancy, which suggests a forgotten associated paraneoplastic syndrome. It has also been suggested that the risk of a second malignancy in thymoma patients is intrinsic and unrelated to other oncogenic factors. We have found that thymic carcinoma, especially neuroendocrine carcinoma, also has a higher incidence of associated malignancy. Thus, long-term follow-up of patients harboring thymic carcinoma is recommended. Because most patients with thymic carcinoma are identified at an advanced stage without specific signs or symptoms, finding a biomarker for early detection of this egregious cancer is of paramount importance.
Histology and specific stains for differential diagnosis According to the WHO classification, type C thymoma comprises a large number of histological types of thymic carcinoma. Because most of these cancers clinically resemble cancers from other organ sites, thymic carcinoma should always be a diagnosis of exclusion. Metastasis from other organs should be ruled out before establishing the diagnosis. Differentiation of thymic carcinoma from cancer metastasized from other organs is still difficult. It has been reported that lymphoid markers expressed in the tumor cells of thymic carcinoma, such as CD5 and CD70, are markers for differential diagnosis; however, they are valid only for differentiating thymic carcinoma from thymoma. Overexpression of c-kit (CD117) in thymic carcinoma is a promising finding because most types of thymoma and squamous cell carcinomas from other organ systems do not express this marker, and squamous cell carcinoma is the most common type of thymic carcinoma.
Staging The Masaoka staging system is the most popular and most widely accepted system for staging and predicting thymoma prognosis. However, because most patients with thymic carcinoma are at an advanced stage (in our series, 1 patient in Stage I, 3 patients in Stage II, 45 patients in Stage III and 29 patients in Stage IV), the usefulness of Masaoka staging for thymic carcinoma is doubtful. Blumberg et al reported that tumor invasion of brachiocephalic vessels indicates a poor prognosis. We also found that invasion of the great vessels indicated a poor prognosis in thymic carcinoma. Unfortunately, both studies contained some patients with type B3 thymoma. Although invasion of the great vessels has been used in the Masaoka staging system as a subcategory of Stage III, this has not been well accepted in recent years. The tumor, node, metastasis (TNM) system has been proposed for evaluating thymoma. Although lymph node metastasis occurs more frequently in thymic carcinoma than in thymoma, the incidence is still low, which makes it difficult to apply the TNM system to thymic carcinoma. A new refined staging for precisely predicting the prognosis of thymic carcinoma is required.