Bladder cancer is a malignancy of the organ in the lower abdomen that stores urine and is the sixth most common cancer in the U.S. Bladder cancer frequently starts in the cells lining the bladder (urothelial cells); however, it can also occur in other types of bladder cells as well as include more than one type of cell.
Three types of bladder cancer that begin in the cells lining the bladder (urothelial cells) are 1) urothelial carcinoma, which is also called transitional cell carcinoma; 2) squamous cell carcinoma; and 3) adenocarcinoma.
Urothelial carcinoma (Transitional cell carcinoma) – Urothelial carcinoma, which is the most common type of bladder cancer in the U.S., is found in the cells lining the inside of the bladder (urothelial), which expand when the bladder is full and contract when it is empty.
Squamous cell carcinoma – Squamous cell carcinoma can occur from chronic bladder irritation, such as frequent bladder infections or long-term catheterization. While rare in the U.S., this cancer is common in other countries where parasite infections called schistosomiasis cause frequent bladder infections.
Adenocarcinoma – Adenocarcinoma occurs in the glands of the bladder that secrete mucus and is rare in the U.S.
Bladder cancer is further classified as either non-muscle invasive bladder cancer (NMIBC) or muscle-invasive bladder cancer (MIBC).
Non-muscle invasive bladder cancer (NMIBC) – Non-muscle invasive bladder cancer is the most common type of bladder cancer, and usually does not spread (metastasize); however, it frequently recurs after treatment.
Muscle-invasive bladder cancer (MIBC) – Muscle-invasive bladder cancer spreads to the muscle wall of the bladder and can be life-threatening.
Bladder cancer is also categorized by the following stages:
Stage 0 (0a and Ois) – Non-invasive papillary carcinoma or carcinoma in situ, with abnormal cells that may become cancerous and spread (metastasize).
Stage I – Cancer has spread to the connective beyond the inner lining of the bladder (urothelial cells).
Stage II – Cancer has spread to the muscle layers of the bladder.
Stage III (IIIA and IIIB) – Cancer has spread to the fat outside the bladder, and possibly the reproductive organs, such as uterus, vagina, prostate, or seminal vesicles; or cancer has spread to one pelvic lymph node.
Stage IV (IVA an IVB) – Cancer has spread from bladder to the lining of the abdomen (peritoneum) or pelvis; or cancer has spread to lymph nodes above common iliac arteries. Cancer has spread (metastasized) to other parts of the body, such as liver, lung, and bone.
Bladder cancers are further categorized based on the appearance of cells, as either a low-grade bladder tumor or high-grade bladder tumor.
Low-grade bladder tumor – Low-grade bladder tumor has cells that look more like normal cells, grows slowly, and is usually non-invasive (does not spread).
High-grade bladder tumor – High-grade bladder tumor has cells that look abnormal, is more aggressive, and is usually invasive (spreads).
The stage and grade of bladder cancer determines its treatment and outcome (prognosis).