Metastasis – How Cancer Spreads

Know these basic facts about spread of cancer.

  • Virtually all cancers spread to other parts of the body.
  • The spread of cancer is called metastasis, the plural of which is metastases.
  • Once the cancer has spread, it is called metastatic cancer.
  • Chances of survival decrease once the cancer spreads or has metastasized.
  • Death more often than not occurs due to metastasis and not from the primary tumor or primary cancer, which is the cancer that first originates in the body. For example, in a patient where the stomach cancer has given rise to metastasis in the liver, the patient will die of liver failure and not stomach cancer.
  • It is often during the late stages of cancer that metastasis occurs.

Metastatic Cancer | How Cancer Spreads

There are five ways in which metastases occurs:

1) Local Metastasis or Direct invasion of cancer

This is metastasis where the cancer cells of the malignant tumor spread and invade the neighboring tissues. Below is an image of local metastasis where T1 stands for tumor 1 and T4 stands for tumor 4.

Picture showing local metastasis in case of prostrate cancer.

local metastasis

2) Lymphatic Spread of Cancer

This is also called embolization and  is the more common type of metastasis wherein the detached cancer cells from the primary cancer tumor, travel via the lymphatic system and get lodged in the lymph nodes to form the growth of secondary tumor. The lymphatic system is a distribution channel of a fluid called lymph, which consists of lymphatic vessels and lymphatic nodes. The lymph carries among other things, the lymphocytes, which are the immune cells responsible for immunity of our body, to the various parts of the body.

3) Metastasis through the blood circulation system

Once the primary malignant tumor during its growth, invades a neighboring blood vessel, the detached cancer cells travel through the blood stream and get lodged in another organ or body tissue. All the cancer cells that travel through the blood do not survive our immune system. But just one cancer cell is enough to grow into a secondary malignant growth. Metastasis through blood takes place through the veins and not the arteries. This metastasis through the blood is called Hematogeneous Spread of Cancer or Hematogeneous  metastasis.

Picture showing metastasis through blood and lymph

metastasis blood lymph

4) Transcoelomic spread of Cancer

Transcoelomic type of metastasis or spread of cancer occurs across cavities such as

  • Transcoelomic spread of cancer through the bronchi which are the airways in the lungs,
  • Transcoelomic spread of cancer through the Pleural Cavity, which is the cavity present between the two layers of the pleural sac and contains the pleural fluid. The pleural sac is the covering sac of the lungs.
  • Transcoelomic spread of cancer through the pericardium which is the sac covering the heart and contains the pericardial fluid. This spread of cancer cells through the pericardium is rare.
  • Transcoelomic spread of cancer through the peritoneal cavity, which consists of the peritoneal sac which covers the abdominal cavity and contains the peritoneal fluid.

Two examples of  Transcoelomic metastasis will

a) An ovarian tumor which spreads through the peritoneal cavity.

b) A mesothelioma, which is a malignant tumor seen in the pleura and spreads through the pleural cavity. This malignancy is an occupational hazard, caused by regular and over exposure to asbestos or glass fragments and powder.

5) Spread of Cancer Cells by Transplantation.

This spread of cancer cells is caused due to mechanical transfer of cancer cells through surgical instruments during surgery or through a needle during an investigative biopsy.

Common Metastatic Cancers or Common Primary Cancers that Spread

Cancer type                                Main sites of metastasis
Breast                                         Lungs, liver, bones
Colon                                           Liver, peritoneum, lungs
Kidney                                        Lungs, liver, bones
Lungs                                          Adrenal gland, liver,
Melanoma                                 Lungs, skin, muscle, liver
Ovary                                         Peritoneum, liver, lungs
Pancreas                                    Liver, lungs, peritoneum
Prostate                                     Bones, lungs, liver
Rectum                                      Liver, lungs, adrenal gland
Stomach                                    Liver, peritoneum, lungs
Thyroid                                     Lungs, liver, bones
Uterus                                        Liver, lungs, peritoneum

Symptoms and Signs of Metastasis

Symptoms and Signs of metastasis of cancer vary according to the organ involved in metastasis. A few examples are given below.

  • Symptoms of Metastasis in Lung are cough, haemoptasis (blood in sputum), and dyspnoea (shortness of breadth).
  • Symptoms and signs of metastasis in the liver are an enlarged liver (hepatomegaly ) and jaundice ( yellowish discoloration of the eyes.
  • Symptoms of metastasis in the brain are headache, seizures(fits) and vertigo( a feeling of dizziness).
  • Symptoms of metastasis in the bones are fracture of the affected bone and bone pain.
  • Signs and Symptoms of Lymph node metastasis shows an enlarged lymph node which is recognized on touch and examination. This is called lymphadenopathy.

Diagnosis of Metastasis

Pathologically, a secondary tumor formed as a result of metastasis is similar to the primary tumor. For example, a primary malignant tumor in the breast will metastasize in the lung. The tissue of this secondary tumor in the lung will be similar to the tissue of the primary tumor in the breast and will not resemble a tissue of lung cancer tumor. This helps the doctor or the oncologist to diagnose and locate the primary cancer.

It is therefore that the cancer is named not according to site of metastasis but according to the site of origin of cancer. For example, a testicular cancer which has  metastasized in the lungs, is called testicular cancer and not lung cancer.

At times, on late presentation by the patient, a secondary tumor may be seen at the time of identification of the primary tumor.  At other times, the secondary tumor may be seen much later, even months or years later.
Sometimes the secondary tumor is detected and diagnosed, while its source, the primary tumor is never found by the doctor. This called Cancer of Unknown Primary Origin or CUP.

Treatment of Metastasis

Besides the treatment of the primary malignancy, which includes

  • supportive treatment for symptoms,
  • surgery,
  • chemotherapy,
  • radiation, or
  • combination of the above,

incidence of metastasis is curtailed by the administration of forskolin or its analogues. Forskolin is a potent inhibitor of platelet aggregation. It is administered alone or with other drugs which inhibit aggregation of platelets. It should be known here that platelet aggregation or clumping plays an important part in the formation of the secondary tumor which has been metastasized through the blood.

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