Tumors and Cancers

Head – Neck – Heart – Lung – Gut

Dongyou Liu

• Editorial: CRC Press
• Año: 2017
• ISBN:
  9781351614412
• Edición: 1
• Categoría: Ciencias biológicas
• Categoría: Biología celular

Tumors and cancers are insidious diseases characterized by uncontrolled growth of abnormal cells that extend beyond their usual boundaries and disrupt the normal functions of affected organs. Forming the second of the four volumes devoted to tumors and cancers, this volume focuses on the head/neck, cardiovascular, respiratory and digestive systems. Each chapter presents a state of the art summary of tumor/cancer of a particular organ/type in relation to its definition, biology, epidemiology, disease mechanism/pathogenesis, clinical signs, diagnosis, treatment and prognosis.

1

Introductory Remarks

1.1 Preamble

Tumors or cancers are insidious diseases that result from uncontrolled growth of abnormal cells in one or more parts of the body.^* Tumors and cancers have acquired a notorious reputation due not only to their ability to exploit host cellular machineries for their own advantage but also to their potential to cause human misery.

With a rapidly aging world population, widespread oncogenic viruses, and constant environmental pollution and destruction, tumors and cancers are poised to exert an increasingly severe toll on human health and well-being. There is a burgeoning interest from health professionals and the general public in learning about tumor and cancer mechanisms, clinical features, diagnosis, treatment, and prognosis. The following pages in the current volume, as well as those in the sister volumes, represent a concerted effort to satisfy this critical need.

1.2 Tumor mechanisms

The human body is composed of various types of cells that grow, divide, and die in an orderly fashion (so-called apoptosis). However, when some cells in the body change their growth patterns and fail to undergo apoptosis, they often produce a solid and sometimes nonsolid tumor (as in the blood). A tumor is considered benign if it grows but does not spread beyond the immediate area in which it arises. Although most benign tumors are not life-threatening, those found in the brain can be deadly. In addition, some benign tumors are precancerous, with the propensity to become cancer if left untreated. By contrast, a tumor is considered malignant and cancerous if it grows continuously and spreads to surrounding areas and other parts of the body through the blood or lymph system.

A tumor located in its original (primary) site is known as a primary tumor. Cancer that spreads from its original (primary) site via the neighboring tissue, the bloodstream, or the lymphatic system to another site of the body is called metastatic cancer (or secondary cancer). Metastatic cancer has the same name and the same type of cancer cells as the primary cancer. For instance, metastatic cancer in the brain that originates from breast cancer is known as metastatic breast cancer, not brain cancer.

Typically, tumors and cancers form in tissues after the cells undergo genetic mutations that lead to abnormal changes known as hyperplasia, metaplasia, dysplasia, neoplasia, and anaplasia (see Glossary). Factors contributing to genetic mutations in the cells may be chemical (e.g., cigarette smoking, asbestos, paint, dye, bitumen, mineral oil, nickel, arsenic, aflatoxin, wood dust), physical (e.g., sun, heat, radiation, chronic trauma), viral (e.g., EBV, HBV, HPV, HTLV-1), immunological (e.g., AIDS, transplantation), endocrine (e.g., excessive endogenous or exogenous hormones), or hereditary (e.g., familial inherited disorders).

In essence, tumorigenesis is a cumulative process that demonstrates several notable hallmarks, including (i) sustaining proliferative signaling, (ii) activating local invasion and metastasis, (iii) resisting apoptosis and enabling replicative immortality, (iv) inducing angiogenesis and inflammation, (v) evading immune destruction, (vi) deregulating cellular energetics, and (vii) genome instability and mutation.

1.3 Tumor classification, grading, and staging

Tumors and cancers are usually named for the organs or tissues in which they originate (e.g., brain cancer, breast cancer, lung cancer, lymphoma, skin cancer, etc.). Depending on the type of tissue involved, tumors and cancers are grouped into a number of broad categories: (i) carcinoma (involving the epithelium), (ii) sarcoma (involving soft tissue), (iii) leukemia (involving blood-forming tissue), (iv) lymphoma (involving lymphocytes), (v) myeloma (involving plasma cells), (vi) melanoma (involving melanocytes), (vii) central nervous system cancer (involving the brain or spinal cord), (viii) germ cell tumor (involving cells that give rise to sperm or eggs), (ix) neuroendocrine tumor (involving hormone-releasing cells), and (x) carcinoid tumor (a variant of neuroendocrine tumor found in the intestine).

Tumors of the head and neck include those affecting the ears, eyes, larynx, lips and oral cavity, nasal cavity and paranasal sinus, odontogenic apparatus, pharynx (nasopharynx, oropharynx, and hypopharynx), and salivary glands [1]. Tumors of the cardiovascular and respiratory systems include those affecting the heart, pleura, and lungs [2]. Tumors of the digestive system include those affecting the anus, appendix, bile duct, colon and rectum, esophagus, gallbladder, liver, pancreas, small intestine, and stomach [3].

Under the auspices of the World Health Organization (WHO), the International Classification of Diseases for Oncology, 3rd edition (ICD-O-3) has utilized a five-digit system to classify tumors, with the first four digits being morphology code and the fifth digit being behavior code [4]. The fifth-digit behavior codes for neoplasms include the following range: /0 benign; /1 benign or malignant; /2 carcinoma in situ; /3 malignant, primary site; /6 malignant, metastatic site; and /9 malignant, primary or metastatic site. For example, meningioma has an IDC-O code of 9530/0 and is a WHO Grade I tumor; atypical meningioma has an IDC-O code of 9539/1 and is a WHO Grade II tumor; and anaplastic (malignant) meningioma has an IDC-O code of 9530/3 and is a WHO Grade III tumor [4].

To further delineate tumors and cancers and assist in their treatment and prognosis, the pathological stages of solid tumor are often determined by using the TNM system of American Joint Commission on Cancer according to the size and extent of the primary tumor (designated T, ranging from TX, T0, T1, T2, T3 to T4), the number of nearby lymph nodes involved (N, ranging from NX, N0, N1, N2 to N3), and the presence of distant metastasis (M, ranging from MX, M0 to M1) [5]. Therefore, the pathological stage of a given tumor is referred to as T1N0MX or T3N1M0 (with numbers after each letter giving more details about the tumor or cancer). However, for convenience, five less-detailed stages (0, I, II, III, and IV), which are based on results of clinical exam and various tests in the absence of findings during surgery, are used clinically to guide the treatment of solid tumors (see Stage, TNM in Glossary) [5].

Another staging system that is more often used by cancer registries than by doctors divides tumors and cancers into five categories: (i) in situ (abnormal cells are present but have not spread to nearby tissue); (ii) localized (cancer is limited to the place where it started, with no sign that it has spread); (iii) regional (cancer has spread to nearby lymph nodes, tissues, or organs); (iv) distant (cancer has spread to distant parts of the body); and (v) unknown (there is not enough information to figure out the stage).

1.4 Tumor diagnosis

Because most tumors and cancers tend to induce nonspecific, noncharacteristic clinical signs, a variety of procedures and tests are employed during diagnostic work-up. These involve medical history review of the patient and relatives (for clues to potential risk factors that enhance cancer development), complete physiological examination (for lumps and other abnormalities), imaging techniques, histological evaluation of biopsy and tissue, and laboratory analysis.

The most commonly used imaging techniques include magnetic resonance imaging (MRI), computed tomography (CT) scan, positron emission tomography (PET) scan, and ultrasound. In general, both MRI and CT help reveal the precise location and dimension of tumor mass, but MRI appears superior to CT in terms of image resolution. MRI consists of T1-weighted, T2-weighted, fluid-attenuated inversion recovery (FLAIR), and diffusion-weighted imaging (DWI) sequences. T1-weighted images with or without intravenous contrast gadolinium reveal anatomic details of tumor and surrounding tissue; T2-weighted images highlight tissues with high water concentration (e.g., edema), giving them a white or hyperintense appearance; FLAIR sequence enhances the image of a lesion (e.g., edema). DWI sequence assists in visualization of areas of acute infarction. PET uses a radioactive glucose (sugar) to highlight malignant tumor cells due to their more active uptake of glucose than normal cells.

For histological evaluation, biopsy tissue is stained with hematoxylin and eosin or immunohistochemical dyes, and observed under a microscope. This helps detect cellular abnormalities and verify whether tumor/cancer cells are present at the edge of the material removed (positive margins), or not (negative, not involved, clear, or free margins), or whether they are neither negative nor positive (close margins).

Laboratory analysis of tissue and body fluids (e.g., blood, urine) reveals altered levels of substances in the body, including metabolites, enzymes, proteins, and nucleic acids. The most commonly used methods include biochemical tests, fluorescence in situ hybridization, polymerase chain reaction, Southern and Western blot hybridizations, flow cytometry, etc.

1.5 Tumor treatment and prognosis

Standard cancer treatments consist of surgery (for removal of tumor and relieving symptoms associated with tumor), radiotherapy (also called radiation therapy or X-ray therapy; delivered externally through the skin or internally [brachytherapy] for destroying cancer cells or impeding their growth), chemotherapy (for inhibiting the growth of cancer cells, suppressing the body’s hormone production or blocking the effect of the hormone on cancer cells, etc., usually via bloodstream or oral ingestion), and complementary therapies (for enhancing patients’ quality of life and improving their well-being). Depending on the circumstances, surgery may be used in combination with radiotherapy and/or chemotherapy to ensure that any cancer cells remaining in the body are eliminated.

The outcomes of tumor and cancer treatment include (i) cure (no traces of cancer remain after treatment and the cancer will never come back); (ii) remission (the signs and symptoms of cancer are reduced; in a complete remission, all signs and symptoms of cancer disappearing for 5 years or more suggest a cure); and (iii) recurrence (a benign or cancerous tumor comes back after surgical removal and adjunctive therapy).

Prognosis (or chance of recovery) for a given tumor is usually dependent on the location, type, grade of the tumor, patient health status and age, etc. Regardless of tumor and cancer types, patients with lower grade lesions generally have a better prognosis than those with higher grade lesions.

1.6 Future perspectives

Tumors and cancers are a biologically complex disease that is expected to surpass heart disease to become the leading cause of human death throughout the world in the coming decades. Despite extensive past research and development efforts, tumors and cancers remain poorly understood and effective cures remain largely elusive.

The completion of the Human Genome Project in 2003 and the establishment of the Cancer Genome Atlas in 2005 offered the promise of a better understanding of the genetic basis of human tumors and cancers and opened new avenues for developing novel diagnostic techniques and effective therapeutic measures.

Nonetheless, a multitude of factors pose continuing challenges for the ultimate conquering of tumors and cancers. These include the inherent biological complexity and heterogeneity of tumors and cancers, the contribution of various genetic and environmental risk factors, the absence of suitable models for human tumors and cancers, and the difficulty in identifying therapeutic compounds that kill or inhibit cancer cells only and not normal cells. Further effort is necessary to help overcome these obstacles and enhance the well-being of cancer sufferers.

Acknowledgments

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