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TNM staging for breast cancer has been required for ACoS-approved hospitals since 1982.

Tumor size is the primary differential in TNM staging. Use the size of tumor reported on the pathology report for best information. Measure the size of the invasive component to assign T category.

If the size is given by physical examination only, use major TNM T-category headings only (T1, T2, etc .) If size is provided by mammography or pathology report, use subcategories T1a, T1b, etc.

Use TX if the primary tumor was excised at another facility and no information about tumor size is available.

If tumor was found by mammography, or if there is no palpable tumor in the breast, indicate that this is the case.

Do not add together the sizes of pieces of tumor removed at biopsy and at resection. Use the largest size of tumor, even if this is from the biopsy specimen. If no size is stated, record as 999 in the field "Size of Tumor".

If a specific size is not given, record size of tumor as 998 if involvement of breast is described as diffuse or inflammatory carcinoma.

In order to stage the case in the AJCC system, the size of tumor must be recorded.

Multifocal tumors in the same breast that are grossly measureable should be staged according to the size of the largest tumor.

Tumors of different histologies should be considered separate primaries if the difference is at the level of the 3-digit ICD-O morphology code.

If ductal and lobular neoplasms are diagnosed concurrently in different quadrants of the same breast, the ICD-O site code should be C50.9.

Simultaneous bilateral tumors should be staged separately. Simultaneous is defined as being diagnosed within two months.

Clusters or clumps of cancer cells found in axillary fat that are not specifically identified as lymph nodes are considered to be axillary lymph nodes that have lost their architectural configuration.

If a wedge resection of the breast is performed done for diagnosis and a more complete procedure, such as a modified radical mastectomy, is done as cancer-directed surgery, code the more complete surgical procedure. The
surgical code should indicate the status of the primary organ at the completion of the procedure.

Surgery is the most common treatment for breast cancer. If no surgery was performed, indicate the reason in the "Reason for No Surgery" field.

Skin dimpling and nipple retraction do not alter the staging of the tumor, but should be noted. They are caused by tension on Cooper's ligament within the breast.

Adherence, attachment, fixation, induration and thickening are considered clinical evidence of extension to skin or subcutaneous tissue of breast.

Skin edema, peau d'orange, encuirasse, inflammation, skin ulceration indicate extensive skin involvement.

Fixation of breast mass (not further specified) is considered involvement of the pectoralis muscle.

Fixation to pectoral fascia (the covering of the muscle) does not influence stage.

Paget's disease of nipple without an underlying tumor in the breast is staged as "Tis" disease. Paget's with other disease is measured by the size of the underlying tumor.