Thymic carcinoma, or type C thymoma, is a malignancy of the
thymus
The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or ''T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders. ...
. It is a rare
cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
that is often diagnosed at advanced stages. Recurrence following treatment is common, and thymic carcinoma is associated with a poor
prognosis.
Epidemiology
A study examining cases of thymic carcinoma in the United States from 2001 to 2015 found a peak
incidence from 70 to 74 years old and a higher incidence in males compared to females. After thymoma, thymic carcinoma is the second most common type of thymus cancer.
Signs and symptoms
Early-stage thymic carcinoma is generally asymptomatic, and the development of symptoms is indicative of an advanced stage cancer.
Signs and symptoms are non-specific and include chest pain, persistent cough, and difficulty breathing, which are related to progressive tumor compression of anterior chest wall structures.
may be associated with thymic carcinoma.
Thymic carcinoma is rarely associated with
paraneoplastic syndromes
A paraneoplastic syndrome is a syndrome (a set of signs and symptoms) that is the consequence of a tumor in the body (usually a cancerous one), specifically due to the production of chemical signaling molecules (such as hormones or cytokines) by ...
, unlike thymoma which has a strong association with
myasthenia gravis.
Pathology
Both
thymoma
A thymoma is a tumor originating from the epithelial cells of the thymus that is considered a rare malignancy. Thymomas are frequently associated with neuromuscular disorders such as myasthenia gravis; thymoma is found in 20% of patients with m ...
and thymic carcinoma originate from thymic
epithelial cells
Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercell ...
; however, the epithelial cells in thymic carcinoma appear abnormal histologically, as they are infiltrative and not arranged in a lobular pattern as seen in the normal thymus.
Thymic carcinoma represents 20% of tumors derived from thymic epithelial cells. Compared to thymoma, the cells of thymic carcinoma behave aggressively; they are fast growing and have a higher likelihood of systemic spread.
The
World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of ...
separates thymoma into categories from type A to C based on histology, with type C thymoma representing the equivalent of thymic carcinoma.
Thymic carcinoma can be further divided into subtypes based on histopathological features. Though the genetic and molecular profile of thymic carcinoma has been shown to be different from that of thymoma,
immunohistochemical
Immunohistochemistry (IHC) is the most common application of immunostaining. It involves the process of selectively identifying antigens (proteins) in cells of a tissue section by exploiting the principle of antibodies binding specifically to ant ...
cell markers specific for thymic carcinoma have not yet been identified.
Diagnosis
Diagnosis of thymic carcinoma is based on a combination of clinical, radiologic, and biopsy findings. Most early cases are asymptomatic and found incidentally on
chest radiographs as a mass in the anterior
mediastinum. Further evaluation consists of additional imaging, such as
CT,
MRI
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...
, and
PET
A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive appearances, intelligence ...
, and tumor
biopsy
A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, or an interventional cardiologist. The process involves extraction of sample cells or tissues for examination to determine the presence or extent of a dise ...
, which is the
gold standard
A gold standard is a monetary system in which the standard economic unit of account is based on a fixed quantity of gold. The gold standard was the basis for the international monetary system from the 1870s to the early 1920s, and from the l ...
and provides the definitive diagnosis.
Biopsy may be done prior to surgery by
fine needle aspiration
Fine-needle aspiration (FNA) is a diagnostic procedure used to investigate lumps or masses. In this technique, a thin (23–25 gauge (0.52 to 0.64 mm outer diameter)), hollow needle is inserted into the mass for sampling of cells that, aft ...
or during the surgery with concomitant evaluation by the pathologist.
Other carcinomas with malignant spread to the thymus are on the differential diagnosis and must be excluded, as they may appear similar to thymic carcinoma on histopathological examination.
Staging
There is no consensus staging protocol for thymic carcinoma.
Both the
Masaoka staging system, designed for thymoma staging, and the
TNM staging system
The TNM Classification of Malignant Tumors (TNM) is a globally recognised standard for classifying the extent of spread of cancer. It is a classification system of the anatomical extent of tumor cancers. It has gained wide international acceptance ...
have been proposed and used for thymic carcinoma, but consensus has been limited. The Masaoka staging system has been more commonly used, but it has been suggested to have limited applicability as most thymic carcinoma patients present at an advanced stage.
The TNM system predicts prognosis if
lymph node spread is observed;
however, cancer spread to lymph nodes is uncommon.
At the time of diagnosis, cancer spread outside of the chest cavity is estimated at less than 7%.
Treatment
Treatment of thymic carcinoma depends on the stage,
though initial
resection of the entire tumor or surgical debulking is standard. Patients with complete resection of the tumor may undergo subsequent
radiation therapy
Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Radi ...
and may also require
chemotherapy
Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs ( chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemothe ...
.
For those with incomplete tumor resection, chemotherapy with or without radiation therapy followed by repeat surgical resection may be warranted.
Other treatment options include
hormone therapy,
targeted therapy
Targeted therapy or molecularly targeted therapy is one of the major modalities of medical treatment ( pharmacotherapy) for cancer, others being hormonal therapy and cytotoxic chemotherapy. As a form of molecular medicine, targeted therapy blocks ...
, and experimental
immunotherapy
Immunotherapy or biological therapy is the treatment of disease by activating or suppressing the immune system. Immunotherapies designed to elicit or amplify an immune response are classified as ''activation immunotherapies,'' while immunotherap ...
.
Prognosis
As thymic carcinoma tends to be diagnosed at later stages, prognosis tends to be poor, with some studies estimating 30 to 55% of patients survive 5 years following diagnosis.
Recurrence following complete resection is common, with one case series finding a recurrence rate as high as 50%.
References
External links
{{Lymphatic organ and vessel disease
Rare cancers
Lymphatic organ neoplasia