M1: metastasis to distant organs (beyond regional lymph nodes)
Use of an "X" instead of a number or other suffix means that the parameter was not assessed.
Other parameters
G (1–4): the grade of the cancer cells (i.e. they are "low grade" if they appear similar to normal cells, and "high grade" if they appear poorly differentiated)
R (0/1/2): the completeness of the operation (resection-boundaries free of cancer cells or not)