When cancer has metastasized, it means that cancer cells have spread from the original (primary) tumor site to other parts of the body, forming new tumors in different organs or tissues. This process involves cancer cells breaking away from the primary tumor, traveling through the bloodstream or lymphatic system, and establishing secondary tumors elsewhere

. Key points about metastasis include:

• The new tumors formed by metastasis are called metastatic or secondary tumors and consist of cancer cells similar to those in the primary tumor. For example, breast cancer cells that spread to the lungs form metastatic breast cancer in the lungs, not lung cancer

• Metastasis is a complex, multi-step process involving invasion of nearby tissues, entry into blood or lymph vessels, survival during circulation, exit into new tissues, and growth at the new site

• Metastatic cancer is often classified as stage IV cancer and generally indicates a more advanced disease with reduced chances for curative treatment

• While all cancers have the potential to metastasize, the likelihood and speed depend on cancer type, grade, size, location, and treatment history

• Metastatic cancer is different from cancer recurrence (cancer returning after treatment) and second cancers (new, unrelated cancers)

In summary, metastasis means cancer has spread beyond its original location to other parts of the body, creating new tumors that share the characteristics of the initial cancer, which complicates treatment and prognosis