Superficial muscle invasion is defined as less than half-way through the muscle coat (three layers).
Deep muscle invasion is considered half-way or more through the muscle coat.
If the depth of muscle invasion is not stated by the surgeon or pathologist, stage as T2, invasion of superficial muscle.
Guidelines for Jewett Staging
- It is important to have good surgical or biopsy specimens so that muscle layers can be seen and assessed.
- The prognostic dividing line is between B1 and B2, so read carefully the description of the depth of muscle invasion.
- AJC Tumor notation T1 to T4 parallels Jewett stages A, B, C, and D; N (node) and M (metastases) are part of Jewett stage D.
Papillary and in-situ tumors can have a long protracted course with multiple recurrences and then suddenly become invasive.
Distinguishing Noninvasive and Invasive Bladder Cancer
The two main types of bladder cancer are the flat (sessile) variety and the papillary type. Only the flat (sessile) variety is called in situ when tumor has not penetrated the basement membrane. Papillary tumor that has not penetrated the basement membrane is called non-invasive, and pathologists use many different descriptive terms for noninvasive papillary transitional cell carcinoma. Frequently, the pathology report does not contain a definite statement of noninvasion; however, noninvasion can be inferred from the microscopic description. The more commonly used descriptions for noninvasion are listed below. All are considered summary stage in situ.
Definite Statements of Non-invasion
- Non-infiltrating; non-invasive
- No evidence of invasion
- No extension into lamina propria
- No stromal invasion
- No extension into underlying supporting tissue
- Negative lamina propria and superficial muscle
- Negative muscle and (subepithelial) connective tissue
- No infiltrative behavior/component
Note: These descriptions of non-invasion apply to bladder cases only.
Inferred Description of Non-invasion
- No involvement of muscularis propria and no mention of subepithelium/submucosa
- No statement of invasion (microscopic description present)
- (Underlying) Tissue insufficient to judge depth of invasion
- No invasion of bladder wall; no involvement of muscularis propria
- Benign deeper tissue
- Microscopic description problematic for pathologist (non-invasion versus superficial invasion)
- Frond surfaced by transitional cells
- No mural infiltration
- No evidence of invasion (no sampled stroma)