Breast cancer is one of the most common malignant tumors in women. It is called malignant because of the uncontrollable growth, infiltration, and metastasis of the tumor. Because tumors often have no obvious symptoms in their early stages, this results in many patients being in the metastatic stage when they are discovered. Determining the stage of breast cancer is intrinsically helpful for clinicians to develop treatment plans that help patients manage their disease while minimizing side effects.
How is breast cancer staged?
The TNM staging of breast cancer is the most common staging system used internationally. It was proposed by the Frenchman Pirerre Denoix between 1943 and 1952, and later by the American Joint Committee on Cancer (AJCC) and the Union for International Cancer Control (UICC). Cancer Control (UICC) gradually began to establish international staging standards, and it has now become the standard method for clinicians and medical researchers to stage malignant tumors.
Breast cancer TNM staging, which is simply defined by the degree of tumor progression, is determined by three main aspects:
- The growth of the tumor itself, that is, the size of the tumor and the extent of its growth infiltration, expressed as T (Tumor);
- The extent of regional lymph node metastasis, including the first station lymph node metastasis and the presence or absence of second station metastasis, expressed as N (Node);
- The presence or absence of distant organ metastasis, indicated by M (Metastasis).
Adding numbers such as 0.1.2.3 below the letters TNM indicates the degree of change, so that the combination of letters plus numbers gives an overall clinical picture of the tumor.
There are usually four stages of TNM: stage I, II, III, and IV. Stage I is a relatively early stage tumor with a good prognosis, while stage IV is the most advanced, with a poor prognosis, and is generally a late stage of the tumor. Many tumor patients have no first symptoms and are only discovered when there is discomfort at the metastatic site, for example, patients with brain metastases from breast cancer cancer will visit the doctor with symptoms of intracranial hypertension such as vomiting and do a whole-body examination before they realize that the primary site is the breast, which is already at an advanced stage of breast cancer.
What does T-staging involve?
The following table shows the specifics of T-staging of breast cancer:
| Tx | Primary tumor could not be evaluated |
| T0 |
No evidence of primary tumor |
| Tis | Carcinoma in situ |
| Tis(DCIS) | Ductal carcinoma in situ |
| Tis(Paget’s) | Paget’s disease of the nipple without a mass |
Note: Paget’s disease with masses is classified by tumor size.
| T1 | Tumor maximum diameter ≤ 2 cm |
| T1mi | microinvasive carcinoma with a maximum diameter of ≤0.1 cm |
| T1a | Tumor maximum diameter>0.1 cm, but ≤0.5 cm |
| T1b | Maximum tumor diameter>0.5 cm, but ≤1 cm |
| T1c |
Tumor maximum diameter>l cm, but ≤2 cm |
| T2 | Tumor maximum diameter>2 cm, but ≤5 cm |
| T3 |
Maximum tumor diameter>5 cm |
| T4 |
Regardless of tumor size, direct invasion of the chest wall (a) or skin (b), as described below |
| T4a |
Invasion of the chest wall, excluding the pectoralis muscle |
| Oedema of the skin of the affected breast (including orange peel-like changes), ulceration, and pathologically confirmed satellite nodules invading the skin also need to be combined with ulceration or edema. | |
| T4c | T4a coexists with T4b |
| T4d |
Inflammatory breast cancer |
With the advancement of technology, the establishment of big human data, and the continuous updating of tumor understanding, the AJCC is also continuously updating and improving the TNM staging system pass, and the latest version as of now is the 8th edition of the AJCC Cancer Staging Manual. The following is a detailed explanation of the key points of the latest T-staging update in breast cancer.
What updates have been made to the eighth edition of the AJCC Cancer Staging Manual for T-staging of breast cancer?
(1) Invasive T-staging
(1) Definition of the largest diameter of invasive cancer
The 8th edition of staging continues to use the TNM system to estimate total tumor volume, where the maximum tumor diameter (T) can be a reasonable means of assessing total tumor volume. If multiple primary lesions are present at the same time, only the diameter of the largest one viewed by the naked eye is counted, and microlesions around the primary lesion that are only visible microscopically are not included in the maximum tumor volume.
(2) Definition of tumor size
If the tumor tissue has both infiltrative and in situ components, the tumor size should be based on the measurement of the infiltrative component. If the tumor tissue consists entirely of ductal carcinoma in situ, the pathologist will try to measure its extent.
Carcinoma in situ with microinfiltration: When microinfiltration is present, the pathologist will note it in the report and measure the maximum diameter of the microinfiltrating foci; in the case of multifocal microinfiltration, the size of the infiltrating foci cannot be cumulative.
In cases of carcinoma in the breast parenchyma with nipple Paget’s disease, the physician staged the tumor according to the size of the parenchymal tumor and noted the presence of Paget’s disease.
(3) Definition of microinvasive carcinoma boundary
The 7th edition of the AJCC breast cancer staging system rounds tumor size in mm, which can affect the determination of microinvasive carcinoma.
In the 8th edition of staging, it was clarified that all microinvasive cancers were ≤1.0 mm (classified as pT1mi for pathologic T-staging) and that the largest invasive cancers of 1.0 to 1.5 mm were recorded as 2.0 mm (classified as pT1a for pathologic T-staging) to avoid “rounding” to pT1mi, which would lead to underestimation of tumor staging.
(4) Multifocal breast cancer
The AJCC defines multifocal breast cancer as a mass in the same quadrant of the same ductal system of origin with two masses at least 5 mm apart. multifocal and multicentric tumors, physicians generally measure size separately.
If the two lesions are largely separated but close together (<5 mm when) and have the same morphology, they likely represent the same lesion. Because of their irregular shape, they appear to be separated. Physicians usually calculate the maximum diameter of the entire lesion as a basis for staging.
(5) Lobular carcinoma in situ (LCIS) removed from the staging system
The 8th edition of staging classified LCIS as benign disease and removed it from pathologic T-stage pTis. LCIS is now considered to be a proliferative disease that is at risk of developing into breast cancer but is not malignantly aggressive in a metastatic way.
There are several subtypes of LCIS, including the pleomorphic subtype, which may have distinct nuclei and nuclear fissures, sometimes with central necrosis or calcification. The pathologic histologic features of pleomorphic LCIS partially overlap with ductal carcinoma in situ (DCIS), including the possibility of calcified foci detected by mammography. After discussion, the panel concluded that the current evidence is insufficient to support the inclusion of pleomorphic LCIS in pTis. pTis can be classified as DCIS if both DCIS and LCIS are present; an alternative early lesion classified as pTis would be Paget’s disease alone, without any invasive or noninvasive carcinoma; if Paget’s disease is associated with rare parenchymal breast LCIS, it may also be counted as pTis.
(6) Definition of T4b
The new guidelines add a clear definition that skin microsatellite nodules should be excluded from the primary tumor and defined as 4b. In the 8th edition of staging, T4b is defined as a satellite nodule with pathologically confirmed skin invasion in addition to skin edema (including orange peel lesions) and ulceration of the affected breast, in addition to ulceration or edema.
The new guidelines add a clear definition that skin microsatellite nodules should be excluded from the primary tumor and defined as 4b.
The new breast cancer staging will help physicians more accurately determine a patient’s condition and assess the extent of their tumor progression so that clinicians can design more appropriate and precise treatment plans for their patients, resulting in better medical care.