T1 bladder cancer is a form of non-muscle invasive bladder cancer (NMIBC) where the tumor has grown through the innermost lining of the bladder and into the connective tissue layer beneath it, but has not yet reached the muscle. This type of bladder cancer accounts for approximately 25% of all bladder cancer diagnoses. T1 bladder cancer is heterogeneous, meaning its behavior can vary greatly among individuals. Some cases may remain less aggressive, while others have a notable potential to progress to more advanced forms of the disease.
Understanding T1 Bladder Cancer
Bladder cancer staging uses the TNM system, where “T” describes the tumor’s extent. For T1 bladder cancer, “T1” indicates the tumor has invaded the lamina propria, the connective tissue directly under the urothelium, the inner lining of the bladder. This distinguishes it from Ta tumors, which are superficial papillary growths confined to the urothelium, and carcinoma in situ (Tis), a flat, high-grade cancer on the surface. T1 bladder cancer is also distinct from muscle-invasive bladder cancer (MIBC), such as T2, where the tumor has grown into the muscle layer.
Tumor “grade” is another classification, referring to how abnormal cancer cells look under a microscope and how quickly they multiply. Bladder cancers are classified as low-grade or high-grade. High-grade T1 tumors are more aggressive, exhibiting a higher likelihood of both recurrence and progression to muscle-invasive disease. In contrast, low-grade tumors grow more slowly and are less likely to spread.
How T1 Bladder Cancer is Diagnosed and Assessed
The procedure for diagnosing and treating T1 bladder cancer is a Transurethral Resection of Bladder Tumor (TURBT). During a TURBT, a surgeon inserts a thin, lighted instrument with a camera, called a resectoscope, through the urethra into the bladder. This instrument visualizes and removes any visible tumors from the bladder wall. The removed tissue is then sent to a pathologist for examination, who determines the cancer’s stage and grade.
A complete TURBT is important for accurate diagnosis and staging, though incomplete initial resections are not uncommon, especially for high-risk non-muscle invasive bladder cancer. For T1 bladder cancer, particularly high-risk cases, a “restaging TURBT” is often recommended 3 to 6 weeks after the initial procedure. This second TURBT helps confirm all visible tumor has been removed and allows for a more accurate assessment of the tumor’s depth of invasion, potentially identifying any remaining disease or unsuspected muscle invasion. The presence of residual tumor at restaging can indicate a higher risk of recurrence and progression.
Pathologists examine the removed tissue for features that influence the patient’s risk of recurrence and progression. These include the depth of invasion within the lamina propria, the presence of carcinoma in situ (CIS), a flat, high-grade cancer on the bladder lining, and tumor multifocality. Tumor size also plays a role, with larger tumors associated with higher risk. The presence of lymphovascular invasion, where cancer cells are found within small blood or lymphatic vessels, suggests a higher likelihood of spread and poorer outcomes.
Treatment Options for T1 Bladder Cancer
Following the initial TURBT, intravesical therapies are employed for T1 bladder cancer, delivered directly into the bladder. An immediate single dose of intravesical chemotherapy, such as Mitomycin C, is often given within hours after the TURBT. This immediate instillation aims to destroy any free-floating cancer cells in the bladder and reduce the risk of tumor recurrence. Mitomycin C is effective in reducing recurrence rates, particularly for low-grade tumors.
For high-risk T1 bladder cancer, Bacillus Calmette-Guérin (BCG) therapy is intravesical immunotherapy. BCG is a weakened form of bacteria instilled into the bladder via a catheter. Once in the bladder, BCG stimulates the immune system to recognize and attack cancer cells.
The schedule involves an initial “induction” course of weekly instillations for six weeks. If the patient responds well, “maintenance” BCG courses may be administered intermittently for one to three years to further reduce the risk of recurrence and progression. Side effects of BCG can include flu-like symptoms, frequent or painful urination, blood in the urine, and fatigue, which usually resolve within a few days. More severe side effects can occur if BCG enters the bloodstream.
Radical cystectomy, the surgical removal of the entire bladder, is a treatment considered for certain T1 bladder cancer cases. This procedure is reserved for high-risk T1 tumors, especially those unresponsive to BCG therapy or that recur after adequate BCG treatment. Factors that might lead to considering early cystectomy include the presence of carcinoma in situ, large tumor size (e.g., greater than 3 cm), multifocal disease, or evidence of lymphovascular invasion. While radical cystectomy offers high rates of cancer-specific survival, it involves surgical morbidity and a recovery period.
Other bladder-sparing approaches, such as partial cystectomy or radiation therapy, are options for selected patients, though they are less common for T1 disease. Partial cystectomy involves removing only the cancerous portion of the bladder, preserving the rest of the organ. This is considered for solitary tumors located in a part of the bladder that allows for complete removal with clear margins. Radiation therapy, sometimes combined with chemotherapy (chemoradiation), can also be used as a bladder-preserving strategy, particularly for patients who are not candidates for or decline surgery. These alternative approaches are evaluated based on individual patient and tumor characteristics.
Monitoring and Long-Term Outlook
Ongoing surveillance is an aspect of managing T1 bladder cancer after initial treatment. The goal of this monitoring is to detect any potential recurrence as early as possible. The follow-up schedule involves regular cystoscopies, which are visual examinations of the bladder using a thin, lighted scope, and urine cytology, a test that checks for cancer cells in urine. These procedures are performed frequently in the initial years after treatment, for example, every three months for the first two years, then every six months for years three to five, and annually thereafter.
Imaging studies, such as CT scans of the abdomen and pelvis, may also be included in the surveillance plan, particularly for high-risk patients or if there are suspicious findings on cystoscopy or cytology. These scans help evaluate the upper urinary tract and detect any distant spread of the cancer, although routine screening for distant metastatic disease in asymptomatic, low-risk patients is not recommended.
While T1 bladder cancer is treatable, there is a risk of recurrence and a potential for progression to more aggressive, muscle-invasive stages. Recurrence rates can be high, with some studies reporting rates between 69% and 80% with TURBT alone, and 35% to 45% with BCG immunotherapy. Progression to muscle-invasive disease occurs in approximately 20% to 40% of T1 bladder cancer cases. Early detection of recurrence and appropriate management are important for achieving long-term outcomes and preserving survival.