Stage 0 cancer, also called carcinoma in situ, has not invaded any local tissue (Tis N0 M0). Stage I cancer is restricted to the oropharynx and the primary tumor is smaller than two centimeters (T1 N0 M0). Stage II cancer is also restricted to the oropharynx, but in this case, the primary tumor is smaller than four centimeters (T2 N0 M0). If the primary tumor grows to over four centimeters, the cancer is upgraded to stage III even in the absence of metastasis or lymphatic spread (T3 N0 M0). A primary tumor of any size accompanied by spread to one lymph node on the same side of the neck is also considered stage III (T1-T3 N1 M0). Stage IVA cancer has invaded structures near the oropharynx with or without spread to lymph nodes (T4a N0-N1 M0). Cancer that has spread to lymph nodes on the opposite side of the neck, cancer that has spread to two or more lymph nodes, and cancer that has spread to one lymph node that is between three and six centimeters, is also stage IVA (T1-T4a N2 M0). Cancer that is more locally invasive than stage IVA cancer is considered stage IVB (T4b N0-N3 M0). Any cancer with no distant metastasis that has spread to lymph nodes larger than six centimeters is considered stage IVB as well (T1-T4 N3 M0). Stage IVC cancer has spread to other organs (T1-T4 N0-N3 M1).