General Characteristics and Macroscopic Appearance
Bladder neoplasms remain a very common cause of urinary tract pathology. Despite significant advances in modern medicine regarding etiology as well as improvements in diagnostic and therapeutic methods, this problem remains highly relevant.
Regarding their origin, the overwhelming majority—about 95%—are of urothelial (transitional cell) origin. A small remaining fraction consists of mesenchymal tumors.
The favored localization of the pathological process is the trigone of bladder, as well as the posterolateral walls of the organ. The macroscopic appearance of the neoplasms is quite diverse: all forms may present 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 pattern of growth, two main forms are distinguished:
- Papillary carcinoma. This is an exophytic tumor connected to the mucosa of the organ by a distinct stalk. An important morphological feature is that invasion of tumor cells beyond the basement membrane is not always present.
- Plaque-like carcinoma. Macroscopically defined as mucosal thickening, lacking distinct papillary (villous) structures. Histological examination may reveal carcinoma in situ, though invasive carcinoma is diagnosed much more frequently. The main difference between plaque-like carcinoma and papillary carcinoma is its pronounced tendency toward the gradual development of cellular anaplasia.
Histological Grading (Differentiation Degree G)
Strict criteria are used to assess the grade of malignancy: cell differentiation, depth of invasion, and extent of the process are taken into account.
- G1 (High differentiation / Low grade). This form accounts for about 50% of all cancers. It is characterized by low 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 intermediate zone are absent, and no mitotic figures are identified.
- G2 (Moderate differentiation / Intermediate grade). The distinction between the superficial, intermediate, and basal zones is completely lost (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, may be found within the tumor tissue.
- G3 (Low differentiation / High grade). Characterized by a disordered arrangement of cells. Atypia and cellular polymorphism are very pronounced. Cell nuclei become hyperchromatic, and high mitotic activity is recorded. Signs of metaplasia persist within the tumor tissue.
Squamous Cell Carcinoma of the Bladder
This tumor type accounts for only 3–5% of all bladder neoplasms. Pure forms of squamous cell carcinoma are much rarer than mixed transitional cell carcinomas containing foci of squamous metaplasia.
Pathophysiologically, the tumor develops primarily in areas of the urothelium that have previously undergone squamous metaplasia.
Morhpologically, the tumor is characterized by a predominantly invasive, infiltrative growth pattern often accompanied by ulceration. Notably, a papillary growth pattern is virtually absent in this type of cancer. Although in situ forms can occur, the tumor most frequently behaves extremely aggressively and involves large areas of the bladder wall.
The histological picture and degree of differentiation vary widely. Well-differentiated carcinomas reveal numerous "cancer pearls" composed of keratohyalin. In anaplastic carcinomas, signs of squamous differentiation may be almost entirely absent.
TNM Classification (T Category)
Staging the extent (invasion) of bladder cancer is of critical importance. Within the T (Tumor) category, the initial stages include:
- Ta — non-invasive papillary carcinoma that does not invade the underlying connective tissue.
- T1 — tumor tissue extends into the lamina propria, but invasion is limited and does not extend deeper than the submucosa.