T4 Breast Cancer Classification
T4 breast cancer is defined as a tumor of any size with direct extension to the chest wall and/or skin involvement (ulceration or skin nodules), and is subdivided into four distinct categories: T4a (chest wall extension), T4b (skin ulceration/satellite nodules/edema), T4c (both T4a and T4b), and T4d (inflammatory carcinoma). 1
T4 Subcategories
T4a: Chest Wall Extension
- Extension to the chest wall, specifically excluding pectoralis muscle adherence or invasion alone 1
- The chest wall includes the ribs, intercostal muscles, and serratus anterior muscle 1
- Pectoralis muscle involvement by itself does not qualify as T4a 1
T4b: Skin Involvement (Non-Inflammatory)
- Ulceration of the skin and/or ipsilateral satellite skin nodules and/or edema (including peau d'orange) of the skin 1
- These findings must be clinically evident and do not meet criteria for inflammatory carcinoma 1, 2
- Important caveat: Nipple retraction is explicitly excluded from T4b classification 2
- Dimpling of the skin or nipple retraction may occur in T1, T2, or T3 tumors without changing their classification 2
- Nipple retraction represents secondary skin change from tumor traction or fibrosis, not the aggressive skin involvement that characterizes T4b disease 2
T4c: Combined Features
- Both T4a and T4b features present simultaneously 1
T4d: Inflammatory Carcinoma
- Inflammatory carcinoma, which is a distinct clinicopathologic entity 1
- This represents the most aggressive form of T4 disease 3
- Characterized by diffuse erythema and edema (peau d'orange) involving at least one-third of the breast skin 3
Critical Clinical Distinctions
Size Independence
- T4 classification is independent of tumor size 1
- A tumor can be very small (even <3 cm) and still be classified as T4 if it meets the skin or chest wall involvement criteria 4
- Small T4 tumors (≤3 cm) may have better prognosis than larger T4 tumors, with 5-year survival of 71.3% versus 34.7% 4
Staging Implications
- T4 disease corresponds to Stage III breast cancer when combined with appropriate N and M classifications 3
- Stage IIIB specifically includes T4N0-2M0, representing inoperable locally advanced disease 3
- Any T4 tumor with N2-N3 nodal involvement or any T with N3 involvement constitutes Stage IIIC disease 3
Common Pitfalls to Avoid
Do not classify nipple retraction or simple skin dimpling as T4b 2
- These secondary skin changes should prompt staging based on actual tumor size (T1-T3) 2
Do not confuse pectoralis muscle invasion with chest wall extension 1
- Pectoralis muscle adherence or invasion alone does not qualify as T4a 1
Distinguish T4b from T4d carefully 1