Types of Bladder Cancer
More than 90% of bladder cancer are transitional cell carcinomas and less frequent malignant tumors arising from bladder are squamous cell carcinoma (5%), adenocarcinoma (3%) and undifferentiated carcinomas (like small cell carcinoma and giant cell carcinoma; 1%). Sarcoma, melanoma and lymphomas of the bladder are extremely rare. Some patients develop mixed-cellularity type of cancers with transitional cell predominance. The TCCs have a tendency for high chance of recurrence, progression of pathologic stages and to develop in multiple sites simultaneously.
Transitional cell carcinoma of the urethra can develop simultaneously or later in about 15% of the patients with bladder cancer. Increased urethral involvement is seen in association with carcinoma in situ (CIS) involving the bladder neck.
The bladder tumors can be broadly grouped in to three categories which can differ in the clinical behavior, the primary treatment and the response to treatment. The groups are superficial, muscle-invasive and metastatic type.
Most of the newly detected bladder cancers are the superficial type and majority are exophytic papillary TCCs. Superficial tumors are graded as low grade (G1), intermediate grade (G2), or high (G3) grade. Grading of superficial type tumors is more important for management unlike the invasive tumors which are almost always high grade type. The low grade exophytic papillary carcinomas resemble the normal urothelium and are considered to be like benign tumors as it rarely progress to higher stages.
The grade G3 superficial tumors are likely to advance to higher stages at a faster pace and require more aggressive treatment strategies to control them. In tumors that are suspected to be invading the lamina propria, the evidence for any invasion of muscularis propria is carefully checked for during the pathological examination.
Staging of Bladder Cancer
The staging of bladder cancer is done with the TNM system of the American Joint Committee on Cancer. The primary cancer of the bladder is staged based on the depth of invasion into the bladder wall. A carcinoma in situ is staged as Tis and is believed to lead to more invasive tumors. About 60% of such tumors, if left untreated, will develop into invasive disease with in 5 years.
An exophytic papillary tumor that is confined to the mucosa is Ta and tumor and if it invades the lamina propria is T1. The lamina propria differentiates the non-invasive tumors (Ta) and invasive tumors (T1). The muscularis mucosa separates the T2 tumors from higher stages. Tumors that invade the muscularis propria are T2 and those invading the perivesicular fat beyond the muscularis propria are T3. Bladder tumors extending to the adjacent organs are T4.
Stage 0 is Ta or Tis and stage I includes the T1 tumors. Stage II and stage III are T2 and T3 tumors respectively, without involvement of any lymph nodes or metastases. Stage IV includes all T4 tumor and tumors of any other stage with lymph node spread or metastasis.