Bladder tumors

General characteristics and macroscopic picture

Bladder neoplasms remain a very frequent cause of urinary tract pathology. Despite significant advances in modern medicine in studying etiology and improving diagnostic and treatment methods, this problem remains highly relevant.

Regarding the origin of the tumors, the vast majority—about 95%—are of urothelial (transitional cell) origin. The remaining small share consists of mesenchymal tumors.

A favored site for the pathological process is the trigone of bladder, as well as the posterolateral walls of the organ. The macroscopic picture of the neoplasms is quite diverse: all forms may appear as coarse villous, plaque-like, exophytic, or invasive growths.

Transitional cell carcinoma (Urothelial carcinoma)

This histological type accounts for up to 90% of all bladder carcinomas. Depending on the growth pattern, two main forms are distinguished:

1. Papillary carcinoma. This is an exophytic tumor attached to the mucosal lining of the organ by a distinct stalk. An important morphological feature is that invasion of tumor cells beyond the basement membrane does not always occur.
2. Plaque-like carcinoma. Macrscopically defined as mucosal thickening, while distinct papillary (villous) structures are absent. Histological examination may reveal a picture of carcinoma in situ, although invasive cancer is diagnosed much more frequently. The main difference between plaque-like and papillary carcinoma lies in its pronounced tendency toward the gradual development of cellular anaplasia.

Histological grading (Degree of differentiation G)

Strict criteria are used to assess the grade of malignancy: cell differentiation degree, invasion stage, and process extent are taken into account.

• G1 (High degree of differentiation). This form accounts for about 50% of all cancer cases. It is characterized by a low grade of malignancy and predominantly exophytic growth. The urothelium covering the villi shows only minimal signs of cellular atypia. The villous lining is thickened and contains more than 7 cell layers. Normal distinctions between the basal layer and the intermediate zone are absent, and mitotic figures are not detected.
• G2 (Moderate degree of differentiation). The distinction between the superficial, intermediate, and basal zones is completely obliterated (this is characteristic of both villous and plaque-like growth). Distinct signs of cellular atypia and polymorphism appear. Foci of squamous and/or glandular metaplasia, as well as mitotic figures, can be found in the tumor tissue.
• G3 (Low degree of differentiation). Characterized by a haphazard arrangement of cells. Atypia and cellular polymorphism are very pronounced. Cell nuclei become hyperchromatic, and high mitotic activity is recorded. At the same time, signs of metaplasia persist in the tumor tissue.

Squamous cell carcinoma of the urinary bladder

This tumor type accounts for only 3–5% of all organ neoplasms. Pure forms of squamous cell carcinoma are much rarer than mixed transitional cell carcinomas containing foci of squamous metaplasia.

The etiopathogenesis is based on tumor development primarily in areas of the urothelium where squamous metaplasia has previously occurred.

Morphologically, the tumor is characterized by a predominantly invasive, infiltrating growth pattern, often accompanied by ulceration. It is important to note that a papillary growth pattern is practically non-existent for this type of cancer. Although an in situ form may be observed, the tumor most often behaves extremely aggressively and affects large areas of the bladder wall.

The histological picture and degree of differentiation vary widely. In well-differentiated carcinoma, numerous "cancer pearls" consisting of keratohyalin are found. In anaplastic carcinoma, signs of squamous differentiation may be almost completely absent.

TNM classification (T category)

Assessment of the stage of spread (invasion) of bladder cancer is of key importance. Within the T (Tumor) category, the following initial stages are distinguished:

• Ta — the tumor shows no signs of invasion. This is a non-invasive papillary carcinoma that does not grow into the underlying tissues.
• T1 — tumor tissue begins to spread deep into the wall, but invasion is limited and does not extend deeper than the submucosal layer of the organ.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Morphological characteristics of mesenchymal bladder tumors.
• Differences between carcinoma in situ and invasive plaque-like carcinoma.
• Criteria for assessing deep invasion (stages T2–T4) according to the TNM system.
• Mixed transitional cell carcinomas with foci of squamous metaplasia.
• Mechanisms of anaplasia development in plaque-like carcinoma.

Other topics in the section "Diseases of the Kidneys and Urinary Tract"

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