An abnormal tissue growth on the inner lining of the bladder is generally referred to as a bladder tumor. Finding a mass or growth in the bladder causes anxiety because the term “tumor” is often associated with cancer. However, not all bladder tumors are cancerous. The primary distinction is whether they are benign (non-cancerous) or malignant (cancerous and capable of spreading).
Understanding the Prevalence of Bladder Tumors
The vast majority of growths identified in the bladder prove to be malignant upon pathological examination. True benign bladder tumors, which are non-cancerous tissue growths, are quite uncommon. These genuinely benign masses account for less than one percent of all bladder masses evaluated by specialists.
Due to this high rate of malignancy, any mass found in the bladder is treated with suspicion until proven otherwise. The small percentage of truly benign tumors is overshadowed by the high incidence of malignant growths, particularly urothelial carcinoma. Non-neoplastic lesions, such as those caused by inflammation (cystitis), can also mimic the appearance of a tumor. While these inflammatory lesions are benign, they are not true tumors and are often counted in statistics of benign lesions rather than true benign tumors.
Characteristics of Non-Cancerous Bladder Growths
Growths definitively classified as benign are characterized by specific cellular and behavioral traits. A benign growth does not invade the deeper layers of the bladder wall or spread to distant sites in the body (metastasis). Under a microscope, the cells of a benign tumor appear well-organized, closely resembling normal bladder cells, and possess distinct, uniform borders.
One of the most common benign growths is the papilloma, which arises from the urothelial cells lining the bladder. A subtype called an inverted papilloma is recognized by its smooth surface and tendency to grow inward rather than outward. Other rare types are distinguished by the specific tissue from which they originate.
For example, a leiomyoma develops from the smooth muscle cells within the bladder wall, and a hemangioma is an abnormal accumulation of blood vessels. These non-cancerous masses tend to grow very slowly. They are usually only problematic if they become large enough to obstruct the flow of urine.
Determining Malignancy: The Role of Pathology
Because symptoms like blood in the urine or frequent urination are common to both benign and malignant bladder growths, a definitive diagnosis requires a microscopic examination of the tissue. The necessary tissue sample is typically obtained through Transurethral Resection of Bladder Tumor (TURBT). During this surgical procedure, the mass is removed via the urethra and the entire specimen is sent to a pathologist for analysis.
The pathologist performs two important steps in classifying the growth: staging and grading. Staging determines the depth of tissue invasion, which is the most significant prognostic factor for a malignant tumor. A tumor is considered non-muscle invasive if it is confined to the inner lining or the connective tissue beneath it, but it is more aggressive if it invades the muscle layer of the bladder wall.
Grading assesses how abnormal the tumor cells appear compared to healthy cells, which indicates the potential aggressiveness of a malignant growth. Low-grade tumors have cells that look relatively normal. High-grade tumors have poorly differentiated cells that are more likely to grow and spread quickly.