Effective with cases diagnosed January 1995 forward. Further, if one lesion has a behavior code of in situ and another a behavior code of malignant, still consider this to be a single primary whose behavior is malignant. Multiple lesions of the same histologic type occurring in different sites are considered to be separate primaries unless stated to be metastatic. NOS and the second lesion is a more specific term, such as large cell carcinoma, mucinous adenocarcinoma, or spindle cell sarcoma, consider this to be single primary and code to the more specific term. If the ductal lesion occurs in one breast and the lobular lesion occurs in the opposite breast, these are considered to be two primaries whether diagnosed within two months or not.
Some tumors have more than one histologic pattern.
Any of these mixed histologies are to be considered one primary. If only one histologic type is reported and if both sides of a paired site are involved within two months of diagnosis, a determination must be made as to whether the patient has one or two independent primaries. If it is determined that there are two independent primaries, two records are to be submitted, each with the appropriate laterality and extent of disease information. If it is determined that there is only one primary, laterality should be coded according to the side in which the single primary originated and a single record submitted. If it is impossible to tell in which of the pair the single primary originated, laterality should be coded as a '4' and a single record submitted.