1. Why are all tumours of central nervous system considered to be malignant?
2. Give the classification of tumours of nervous system.
3. Enumerate benign and malignant tumours of melanin-creating tissue.
4. Why do melaninemia and melaninuria occur in melanoma?
Astrocytoma, astroblastoma, oligodendroglioma, oligo-dendroglioblastoma, ependymoma, ependymoblastoma, chorioid papilloma, chorioidcarcinoma, glioblastoma, ganglio-neuroblastoma, medulloblastoma, arachnoidendothelioma, neurilemmoma, nevus, melanoma.
First, it is necessary to emphasize that epithelial tumors are the most frequent ones in the man, they involve chiefly people of middle and old age. Every 6th person over 40 dies from this tumor. In Europe, cancers are 4 times more frequent than in Asia. For instance, stomach cancer affects around 8000 people per year in the UK, although the incidence is declining. It affects more men than women. It is rare under the age of 40 and becomes more common with increasing age. The decline in the rate of stomach cancer is thought to be associated with improvements in diet.
Skin cancer is very rare in children but is more common as people get older. At the age of 20 only about 1 person in 100 000 has non-melanoma skin cancer, whereas at the age of 80 about 200 per 100 000 have it.
The incidence of kidney cancer is increasing and now accounts for approximately 6 000 new cases per year.
Cancer of the ovary is more common in women who have never had children than in those who have. It may occur at any age but is most usual between the ages of 50 and 80. Before age 30, the incidence is less
than 1 in 50 000. After 55 it is about 1 in 2000 women. The incidence peaks in women in their seventies.
Benign epithelial tumors are subdivided according to their origin from different types of epithelium into the tumors of integumentary epithelium (papillomas), tumors of glandular epithelium (adenomas).
Papilloma is a tumor originating from the skin and mucous membranes, it looks like a ledge or a bush of branching papillae. It is a good example of an exophytic tumor. The base of the tumor consists of connective tissue containing blood vessels. It is a continuation of subepithelial connective tissue covered with epithelium like with a glove.
Depending on the stage of the development and the character of stroma, papilloma may be either hard of soft.
Hard papillomas are benign, they grow slowly, seldom become ulcerative and seldom bleed. They appear on the skin and mucous membranes covered with multilayer squamous epithelium (mouth, larynx, pharynx).
Soft papillomas are tender, their stroma is loose, swollen, consists of thin fibers with thin-walled vessels. They are covered with cylindrical transition or ciliated epithelium. Their thin branching papillae can be easily injured and bleed. These papillomas more often occur on the mucous membranes (nose, uterus, gastrointestinal tract, fallopian tubes) and are associated with chronic irritation of the mucous
membrane. The most dangerous are papillomas of the urinary bladder. They grow quickly, relapse, may be the cause of bleeding resulting in general anemia, they often become malignant turning into cancer. These papillomas are mainly found in the neck of the urinary bladder and in the region of the triangle. It is necessary to admit that in papilloma both epithelium and stroma are subjected to tumor growth, they are characterized by anaplasia, therefore papillomas are considered fibroepithelial tumors.
Adenoma is a benign epithelial tumor from the epithelium of the glands and glandular organs. More often they can be found in the breast, thyroid gland, liver, ovaries, prostatic gland, gastrointestinal tract. According to the histological composition adenoma may be tubular and alveolar. In tubular adenoma, there are glandular cavities resembling tubes in the connective tissue with vessels. In alveolar adenoma, numerous bubbles bedded with cylindrical or cubic epithelium are observed in the connective tissue with vessels. In this cases, the epithelium is separated from the surrounding tissue by its own membrane.
Adenomas from compact organs (liver, adrenal gland) can be made of groups of respective cells separated from each other by a thin layer of stroma. Thus, the structure of adenomas is similar to that of the original organ which is the cause of their functional similarity (ability of adenoma cells to produce respective secretes) e.g. - adenomas of mucous
membranes - mucus, adenomas of eosinophilic cell of the anterior lobe of pituitary - somatotropic hormone, medullar layer of adrenal gland - norepinephrine, beta cells of pancreas - insulin, etc. This peculiarity must be always taken into account by a physician as it may contribute timely diagnosis of these tumors and correct treatment tactics. But, alone with similarity, adenomas (being tumors) have atypical structure which manifests in absence of ducts, variety of shape, size and location, parenchyma and stroma ratio (fibroadenoma, adenofibroma) in the glandular tubules and vesicles.
Sometimes papilloid growth of epithelium, bedding glandular cavities, is observed.
In some adenomas glandular cavities are widened and form large cavities, cysts filled with serous fluid or mucus. These cyst-like adenomas are called cystoadenomas.
Sometimes epithelial integument of glandular cavities begin to grow in a cyst-like manner. The papillae fill cyst-like cavities with masses resembling cauliflower.
Sometimes epithelial growth is so intensive that the papillae invade the walls of the cyst, involve the peritoneum, produce metastases, relapse, cause cachexia and may cause sever consequences. These adenomas are termed papillary adenocystomas. They develop in ovaries, thyroid gland. Adenocystomas may become malignant more frequently than the other adenomas.
Immature, or malignant, tumors of epithelium are also called cancers. The term came to us from the time of Hippocrates and Galen.
The popularity of this term can be explained by the increase of the cancer incidence in the 20th century when compared with previous centuries.
This fact can be explained by the increase of the life expectancy by 20 years, that is the group of people of «cancer age» enlarged (due to increased possibility to be exposed to carcinogenic factors, accumulation of the total number of precarcinogenic processes and increased chance to develop latent cancer with long duration). Besides, increase of the number of tumors can be associated with improvements in diagnosis. But the above does not exclude objective causes of cancer development, especially in the population of the developed countries due to increase of the number of industrial tumors (cancer of lungs, skin, urinary bladder) associated with exposure to chemical carcinogens (at present there are about 300 of them, mainly polycyclic aromatic hydrocarbon, azo- or aminocompounds).
The morphological classification is based on differentiation of the tumor cells.
According to it all cancers can be divided into 3 groups:
1) poorly-differentiated: small-cell or basal cell, medullar, scirrhus, solid;
2) well-differentiated: squamous-cell, with keratinization, without keratinization, adenocarcinoma (trabecular, alveolar, papillary, mucous);
3) special kinds: chorionepithelioma, seminoma, hypernephroid cancer.
This classification is important because main clinico-morphological peculiarities of different cancers are due to the degree of differentiation, or anaplasia of their cellular elements: intensity and character of the primary tumor growth, secondary changes, sensitivity to radiotherapy which in higher in undifferentiated, character, rate and terms of metastases appearance. Squamous-cell cancer of skin, bronchi, i.e. highly differentiated cancers, do not produce metastases for a prolonged period of time. Vice verse undifferentiated cancers, e.g. medullar, small-cell cancer of bronchi, even small in size, gives early and abundant metastases. This may be accounted by the location of the cellular complexes in medullar cancers forming pure cultures of free cells easily penetrating lymphatic and blood vessels. It is necessary to remember about the association of the type and character of the metastases with the age of the patient. Thus, the size of the primary tumor does not influence metastases appearance, its histological structure and the degree of anaplasia are more important.
As to metastases, it is important to know that invasion of the tumor cells to the veins is difficult because they become narrowed in the rapidly growing
tumor and due to increase of intravenous pressure. Blood vessels in the tumors look differently. Usually they have the structure of capillaries. As a rule, vessels in tumors are new structures but they are connected with general circulation. The tumors may be connected with the sources of nutrition in different ways. The more directly they contact, the more intensive is the growth of the tumor, the more rapidly it produces metastases (e.g., chorionepithelioma, seminoma, hypernephroid cancer).
If both stroma and parenchyma of the tumor are anaplastic, they characterize combination tumors, termed sarcocarcinomas or carcinosarcomas.
Together with tissue and cellular atypism, malignant tumors are characterized by infiltrating tumor growth.
Clinico-anatomical practice suggests that tumor, as a rule, does not appear at once, its development is preceded by different processes characterized by: 1) prolonged chronic course, 2) association with cell multiplying, 3) failure of conservative treatment.
These kind of processes or states are called precancerous. There are a large number of them: defects of development, including lost embryonic germs, chronic inflammatory diseases, chronic ulcers, disturbed tissue regeneration (abundant granulation, metaplasia), hormonal hyperplasias, polyposis of mucous membrane, leukoplakias of the mucous membrane. The problem of the terms of transition of
pre-cancerous states into cancers is disputable. It is thought that the period of malignization (latent period) may last for 15-20 years (gastric cancer). Clinical observations show that some precancerous states turn into cancers more often than the other. The former are called obligatory precancers (polyposis of the mucous membrane of the stomach, intestine, uterus, chronic gastric ulcer, cystic mastopathy, erosion of the uterine cervix), the latter are optional.