Thymic Carcinoma


What is thymus?

The thymus is one of the major parts of the lymphatic system, which play a key role in production of the lymphocytes (WBC) and improve our immune system. By involving in the production of T-lymphocytes, it acts against infectious agents. (1)

Thymus location

The thymus is a small organ, located in the upper part of the chest cavity, behind the sternum. (1)

Thymic Carcinoma


                                 Thymus location

What is thymic carcinoma?

Thymic carcinoma is not frequently occurring cancerous tumor. It usually develops in the outer lining of the thymus, due to the abnormal cell proliferation.

At the initial stage no difference found between cancerous cell growth and normal cell growth of the thymus, as the cell division is slowly progressive and usually limit the development within the thymus. In rare case, the malignancy is spread away from the thymus.

But in advance stage the cells involve in the thymic carcinoma, is totally differ from normal cells and very fast growing step and usually become metastatic and spread to other adjoining and even distant part from the thymus. Complex treatment and management measures are followed in thymic carcinoma. Along with carcinogenic effects, other immunological disturbance like rheumatoid arthritis or myasthenia gravis may also associated.


Early sign and symptom is not very specific distinguishable, and usually detect eventually during another investigation through chest x-ray or CT scan. (2)

Symptoms

Usually reported as, cases of thymic carcinoma is mostly asymptomatic. Symptomatic differentiation and specificity is not distinguishable with other general respiratory system disorder. The included symptoms are more generalized, which include a chronic coughing, dyspnoea, or pain in chest. These indistinguishable symptoms may responsible for delay diagnosis.


Different types of cells are made thymus and each of which can involve in development of different kinds of malignancy:

  • Thymus is shaped by epithelial cells and one of the prime cells involve in thymic carcinomas.
  • Lymphocytes are other chief cells found in thymus and the involvement of the lymphocytes carcinoma are medically termed as Hodgkin disease and non-Hodgkin lymphoma.
  • Kulchitsky cells are also found in the thymus, which secrete some hormones and cancerous development of these cells are termed as carcinoid tumors. (1)

Staging of thymic carcinoma

Staging is important to estimate the malignancy of the cancerous growth. Depending upon the stage it can estimate that how much cancer is spread apart from the thymus, which helps in preparing the proper treatment plan for the patient.

Thymic cancer is not an usual cancerous growth, therefore much more information is not accumulated and staging of the thymic cancer is controversial. According to the American cancer society, a Masaoka staging system may be a useful method to staging the thymic cancer. Masaoka staging system depends on the following factors:

  • The imaging tool like CT scan or MRI helps to estimate the spreading of the cancerous cells
  • The possibility of the surgical removal of the cancerous tumor or how much the tumor is invasive in nature
  • Malignancy is spread apart from thymus.

According to the Masaoka system, the staging of the thymic carcinom is divided into four main stages.

Stage I

When thymic carcinoma is not spread to the outermost layer and invasion is restricted. Stage I is non-invasive.

Stage II

In stage II, carcinogenicity is spread to other surrounding areas and further divided into two parts II A and IIB.

Stage II A: the cancerous growth is spread to the outer layer of the thymus gland.

Stage II B: The cancerous growth is spread from outer layer of the thymus to the surrounding fatty tissue and may affect the covering of the lungs (mediastinal pleura) or the outer sac of the heart (pericardium).

Stage III

The carcinoma has spread to the lungs, heart or major blood vessels, including the aorta and/or superior vena cava. At this stage tumor become aggressive and spread rapidly towards nearby organs.

Stage IV

This stage is further divided into IV A and IV B.

Stage IV A

The whole pleura and in some cases pericardium is also involved with thymic cancer due to aggressive and fast growth rate.


Stage IV B

In this stage, the metastasis are spread to distant organs and involving liver, lungs and bones. (3)

Treatment

The treatment plan is not same for all the patients suffering from thymic carcinoma. The treatment plan mainly depends upon the stage and the type of the cancer. For this, biopsy test in important. Depending upon this doctor is deciding to the chances of removal of the metastatic mass of the affected part.  Other considerable factors are age, co-morbidity, patient response, etc.

Thymic cancer is not very usual disease and the vast data about the success of treatment or better treatment option is not smoothly decidable. Depending upon the specificity of every case, the possible treatment options are discussed by the team of the experts, including  thoracic surgeon, medical oncologist, radiation oncologist, a neurologist, pulmonologist,  psychologists, nursing head, nursing care provider, rehabilitation specialists, social workers, and other allied healthcare professionals.

The team  also discusses the treatment plan and considerable side effects with patient and patient representative and try to clear all the treatment related query. The available treatment options are, surgery, Radiation therapy and chemotherapy. The thymic carcinoma may be resectable, unresectable.

Stage I and II resectable carcinoma is treated with surgery. Initial diagnosis and successful surgical removal may not need adjuvent therapy, even sometimes radio-surgery can successfully kill the But stage III and IV resectable carcinoma may also need pre and post adjuvent therapy in addition of surgery. Adjuvent therapy can be incorporated through radiation or chemotherapy or both in advance stage.

Unresectable carcinoma cannot be treated with surgery due to the location of the mass or in advance stage, it may spread in such a way that the surgical removal of the mass cannot be possible. In this case combination of radiation and chemotherapy is prescribed to the patient.(4,5)

Survival rate

According to the American cancer society, they provide one data depending upon the 5 year survival rate history collected in the period between 1990 and 1994, conducted in Japan. Initial diagnosis and early stage provide more survival rate than advance stage carcinoma.

Approximately 74% patient reached in ‘5 year survival rate’ in stage I  and II thymic carcinoma, 33% ‘5 year survival rate’ observed in stage III and only 24% patient reached in ‘5 year survival rate’ in stage IV thymic carcinoma.(6)

Prognosis

The prognosis varies with the treatment plan, though yet any established treatment plan is recommended. Some doctors prefer a cisplatin- and/or doxorubicinbased combination of chemotherapeutic agent, whereas some studies provide information about addition of neoadjuvant chemotherapy is better pre-surgical therapy in resectable carcinoma and also improve the survival rate.

Therefore, there is a vast scope of clinical research to establish better treatment option in thymic carcinoma, which provide a better prognosis in future. (7)

References

1. Thymoma and Thymic Carcinoma Treatment–Patient Version (PDQ®), (2015); National Cancer Institute; Retrieve from: http://www.cancer.gov/types/thymoma/patient/thymoma-treatment-pdq

2. Thymoma and Thymic Carcinoma—Patient Version; National Cancer Institute; Retrieve from: http://www.cancer.gov/types/thymoma

3. How is thymus cancer staged? (2014); American Cancer Society; Retrieve from: http://www.cancer.org/cancer/thymuscancer/detailedguide/thymus-cancer-staging

4. How is thymus cancer treated? (2014); American Cancer Society; Retrieve from: http://www.cancer.org/cancer/thymuscancer/detailedguide/thymus-cancer-treating-general-info

5. Treatment of thymus cancers by extent and type of tumor, (2014); American Cancer Society; Retrieve from: http://www.cancer.org/cancer/thymuscancer/detailedguide/thymus-cancer-treating-by-extent

6. Survival rates for thymus cancer (2014); American Cancer Society; Retrieve from: http://www.cancer.org/cancer/thymuscancer/detailedguide/thymus-cancer-survival-rate

7. Kazuhiko Ogawa, Takafumi Toita, Takashi Uno, Nobukazu Fuwa, Yasumasa Kakinohana, Minoru Kamata, Kageharu Koja, Takao Kinjo, Genki Adachi, Sadayuki Murayama, (2002); Treatment and Prognosis of Thymic Carcinoma: A Retrospective Analysis of 40 Cases; American Cancer Society; Retrieve from: http://onlinelibrary.wiley.com/doi/10.1002/cncr.10588/pdf

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