In British English, the verb "metastasize" is often spelled "metastasise."  The "-ise" spelling is the preferred form in British English, while "-ize" is more common in American English. Both spellings are considered correct, but "-ise" is generally used in the UK according to the Online Etymology Dictionary and other British English sources. 

Examples of "metastasis" used in a sentence: 
*"The cancer had metastasized to the lungs, meaning it had spread from its original location to other parts of the body." 
*"The pathologist who evaluates cancer cells in biopsied tissue designates the cancer as being stage I, II, III, or IV, in terms of the degree of metastasis." 
*"Thirty-one patients had a sentinel lymph node positive for melanoma metastasis." 
*"The smallest detected metastasis was a micrometastasis with a diameter of 0.9 cm."
*"Primary bone cancer is much less common than bone metastasis." 
*"It invades surrounding tissue and spreads to nearby or distant organs (metastasis)."

Just the facts:

METASTASIS Definition & Meaning - Merriam-Webster