Cancer is the second leading cause of death in the United States; only cardiovascular disease takes a higher price. Even more distressing than the associated mortality is the physical and emotional suffering inflicted by neoplasms. Patients and the public often ask, “When will there be a cure for cancer?” The answer to this simple question is difficult because cancer is not one disease, but many disorders that share profound growth dysregulation. Some cancers, such as Hodgkin lymphoma, are highly durable, while others, such as pancreatic cancer, are virtually always fatal. The only hope for controlling cancer lies in learning more about its pathogenesis, and great strides have been made in understanding the molecular basis of cancer. This chapter deals with the basic biology of neoplasms: the nature of benign and malignant neoplasms and the molecular basis of neoplastic transformation. The host response to tumors and the clinical features of the neoplasm are also discussed.
Before we discuss What is Neoplasia in Pathology (Robbins) the features of cancer cells and the mechanisms of carcinogenesis, it is useful to summarize the fundamental and shared characteristics of cancers:
Cancer is a genetic disorder caused by DNA mutations
Most pathogenic mutations are induced by exposure to mutagens or occur spontaneously as part of aging. In addition, cancers frequently show epigenetic changes, such as focal increases in DNA methylation and alterations in histone modifications, which in turn may result from acquired mutations in genes that regulate such modifications. These genetic and epigenetic changes alter the expression or function of key genes that regulate fundamental cellular processes, such as growth, survival, and senescence.
Genetic alterations in cancer
Genetic alterations in cancer cells are inherited and are transmitted to daughter cells after cell division. As a result, cells harboring these alterations are subject to Darwinian selection (survival of the fittest, possibly the most important scientific concept in biology). Cells carrying mutations that provide a growth or survival advantage outnumber their neighbors and thus come to dominate the population. At the time of tumor initiation, these selective advantages are conferred on a single cell and, as a result, all tumors are clonal (ie, the progeny of a cell). However, even beyond the point of initiation, Darwinian selection continues to shape the evolution of cancers by favoring the appearance of genetically distinct subclones with more aggressive characteristics, an important concept called progression.
Mutations and epigenetic
Epigenetic mutations and alterations impart to cancer cells a set of properties that are collectively called cancer characteristics. These properties produce the cellular phenotypes that dictate the natural history of cancers, as well as their response to various therapies. The molecular underpinnings of each cancer hallmark are discussed in later sections.
Basic research has elucidated many of the cellular and molecular abnormalities that give rise to cancer and govern its pernicious behavior. These insights, in turn, are leading to a revolution in cancer diagnosis and treatment, an emerging triumph of biomedical science.
Neoplasia literally means “new growth.” Neoplastic cells are said to transform because they continue to replicate, apparently oblivious to the regulatory influences that normal cells control. Neoplasms, therefore, enjoy a certain degree of autonomy and tend to increase in size regardless of their local environment. However, its autonomy is not complete. All neoplasms depend on the host for their nutrition and blood supply. Hormone-responsive tissue-derived neoplasms often require endocrine support as well, and these dependencies can sometimes be exploited therapeutically.
In general, benign tumors are designated by adding the suffix -oma to the type of cell from which the tumor arises. For example, a benign tumor that arises in fibrous tissue is a fibroma; A benign cartilaginous tumor is a chondroma. A more varied and complex nomenclature applies to benign epithelial tumors. The term adenoma is generally applied not only to benign epithelial neoplasms that produce gland-like structures but also to benign epithelial neoplasms that arise from the glands but lack a glandular growth pattern. Therefore, a benign epithelial neoplasm that arises from the cells of the renal tubules and that grows in a gland-like pattern is called an adenoma, as is a mass of benign epithelial cells that do not produce glandular patterns but originate from the adrenal cortex.
Papillomas are benign epithelial neoplasms that grow on any surface and produce microscopic or macroscopic finger-shaped fronds. A polyp is a mass that projects onto a mucosal surface, such as in the intestine, to form a macroscopically visible structure (Fig. 6.1). Although this term is commonly used for benign tumors, some malignant tumors can also grow as polyps, while other polyps (such as nasal polyps) are not neoplastic but are inflammatory in origin. Cystadenomas are hollow cystic masses that normally arise in the ovary.
The nomenclature of malignant tumors essentially follows that of benign tumors, with some additions and exceptions.
- Malignant neoplasms that arise in “solid” mesenchymal tissues or their derivatives are called sarcomas, while those that arise from mesenchymal cells in the blood are called leukemias or lymphomas. Sarcomas are designated based on their cell-type composition, which presumably reflects their cell of origin. Thus, a malignant neoplasm composed of fat-like cells is a liposarcoma, and a malignant neoplasm composed of chondrocyte-like cells is chondrosarcoma.
- Although the epithelia of the body are derived from the three layers of germ cells, malignant epithelial cell neoplasms are called carcinomas regardless of the tissue of origin. Therefore, malignant neoplasms that arise in the renal tubular epithelium (mesoderm), the skin (ectoderm), and the lining epithelium of the intestine (endoderm) are considered carcinomas. In addition, the mesoderm can lead to carcinomas (epithelial), sarcomas (mesenchymal), and hematolymphoid tumors (leukemias and lymphomas).
Carcinomas are further subdivided.
- Carcinomas that grow in a glandular pattern are called adenocarcinomas and those that produce squamous cells are called squamous cell carcinomas. Sometimes the tissue or organ of origin can be identified, as in the designation of renal cell adenocarcinoma, but it is not uncommon for tumors to show little or no differentiation. These tumors are called poorly differentiated or undifferentiated carcinoma.
Cells transformed into a neoplasm, whether benign or malignant, generally resemble each other, according to their origin from a single transformed progenitor cell. In some unusual cases, however, tumor cells undergo divergent differentiation, creating so-called “mixed tumors.” Mixed tumors are still monoclonal in origin, but the progenitor cell in such tumors has the ability to differentiate more than one lineage. The best example is the mixed tumor of the salivary gland. These tumors have obvious epithelial components scattered throughout a fibromyxoid stroma, sometimes harboring islands of cartilage or bone (Fig. 6.2).
All of these diverse elements are believed to be derived from a single transformed epithelial progenitor cell, and the preferred designation for these neoplasms is pleomorphic adenoma. Fibroadenoma of the female breast is another common mixed tumor. This benign tumor contains a mixture of proliferating ductal elements (adenoma) embedded in loose fibrous tissue (fibroma). Unlike pleomorphic adenoma, only the fibrous component is neoplastic, but the term fibroadenoma is still in common use.
Teratoma is a special type of mixed tumor that contains recognizable mature or immature cells or tissues derived from more than one layer of germ cells, and sometimes all three. Teratomas arise from totipotential germ cells, such as those that normally reside in the ovary and testes and are sometimes abnormally present in midline embryonic remains. Germ cells have the ability to differentiate into any of the cell types found in the adult body; It is not surprising, therefore, that they can give rise to neoplasms that contain elements that resemble bone, epithelium, muscle, fat, nerves and other tissues, all grouped in a vertiginous way.
FAQ about Neoplasia
What is neoplasia?
Neoplasia (nee-oh-PLAY-zhuh) is the abnormal and uncontrolled growth of cells or tissues in the body, and the abnormal growth itself is called a neoplasm (nee-oh-PLAZ-m) or tumor. It can be benign (bee-NINE) or malignant.
What is colonic neoplasia?
Colorectal cancer (CRC) is the third most common cancer and the third leading cause of cancer-related death in the United States. It is estimated that approximately 135,000 new cases of CRC will be diagnosed in 2016 and that there will be 50,000 deaths from colorectal cancer.1 Detection of CRC has been associated with a decrease in the incidence and mortality of CRC.2 Unfortunately, only 65% of eligible Americans are updated with recommended screening. Colorectal cancers found in screening tests are more likely to be early stage and curable compared to cancers found in a test done for tumor-related symptoms. Efforts should focus on improving detection rates, recognizing and mitigating risk factors, adhering to evidence-based intervals for colonoscopic surveillance, and improving the quality of colonoscopy.
What is neoplasia in dogs?
Most forms of malignancy will ultimately result in weight loss, apathy, and a reluctance to eat. The specific signs of cancer can vary, depending on the part of the body affected. For example, gastrointestinal cancers often cause vomiting and diarrhea, while tumors of the nervous system can cause seizures.
Early detection of cancer is always important to improve the chances of success if treatment is chosen.
• Abnormal swelling that persists or continues to grow
• Sores that don’t heal
• Loss of appetite
• Bleeding or discharge from anybody opening
• offensive odor
• Difficulty eating or swallowing
• Hesitation to exercise or loss of stamina.
• Persistent limp or stiffness
• Difficulty breathing, urinating or defecating
What are multiple endocrine neoplasias?
Multiple endocrine neoplasia type 1 (MEN1) is an inherited condition associated with tumors of the endocrine (hormone-producing) glands. MEN1 was originally known as Wermer syndrome. The most common tumors seen in MEN1 involve the parathyroid gland, islet cells of the pancreas, and the pituitary gland.
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