Cancer

Cancer (medical term: malignant neoplasm) is a class of diseases in which a group of cells display uncontrolled growth, invasion of adjacent tissues, and sometimes metastasize to other locations in the body. These three malignant properties of cancers differentiate them from benign tumors, which are self-limited, do not invade or metastasize. Most cancers form a tumor but some, like leukemia, do not.

Cancer is not a single disease. There are hundreds of different types of cancers. Oncology is the branch of medicine concerned with the study, diagnosis, treatment, and prevention of cancer.

Cancer may affect people at all ages but the risk increases with age. Cancer causes about 13% of all deaths in the United States. According to the American Cancer Society, 7.6 million people died from cancer in the world in 2007.

Overview

Most cancers are caused by abnormalities in the genes of the cancerous cells. These mutations may be due to the effects of carcinogens, such as tobacco smoke, radiation, chemicals, or infectious agents. Some cancer-causing mutations may be inherited from the parents or may occur spontaneously.

Impaired DNA repair in high-distressed individuals. Kiecolt-Glaser et al., J Behav Med, 1985

Weakness of the immune system or of DNA repair systems, secondary to stress or disease, may also play a role ^[1]. Certain psychological constitutions were followed by either higher or lower cancer incidence of cancer during several decades ^{[2] [3] [4] [5]}. For a cancer to become dangerous, however, several mutations are needed, a process that may take several years. It is therefore usually impossible to attribute a given cancer to a single cause.

Genetic abnormalities found in cancer cells typically affect two classes of genes. Cancer-promoting oncogenes are activated, whereas Tumor suppressor genes ("antioncogenes") are inactivated.

The symptoms of cancer depend on its type and location. In general, symptoms are caused by large, advanced tumors, hence the importance of cancer screening to detect small tumors in persons without symptoms. The definitive diagnosis of cancer usually requires examination of a biopsy specimen by a pathologist. Treatment and the probability of success (prognosis) depends on the type of cancer, its location, and stage. The usual treatment options include surgery, chemotherapy and radiotherapy. Current treatment can improve the survival of almost all patients and many patients can be entirely cured. Psycho-therapy may be a promising additional treatment. In some studies positive effects of psychotherapy on survival were seen in patients with breast cancer, colorectal and other gastro-intestinal cancers as well as melanoma. More information about this on the medpedia Psycho-Oncology pages.

Interestingly, spontaneous remissions have been observed in virtually all types of cancer ^[6], ^[7]. It has been estimated that current breast cancer screening leads to the detection of 30% more breast cancers than otherwise would have become manifest during life ^[8]. Without screening, these extra tumors apparently would have gone unnoticed, either by very slow progression, dormant periods or even spontaneous regression. Some researchers have collected patients with spontaneous regression of advanced cancer in order to discover psychosocial processes, that may be implicated in tumor growth and reversal. More about this under Psycho-Oncology.

Glossary

The following closely related terms may be used to designate abnormal growths:

• Tumor or tumour: originally, it meant any abnormal swelling, lump or mass. In current English, however, the word tumor has become synonymous with neoplasm, specifically solid neoplasm. Note that some neoplasms, such as leukemia, do not form tumors.
• Neoplasm: the scientific term to describe an abnormal proliferation of genetically altered cells. Neoplasms can be benign or malignant:
  • Malignant neoplasm or malignant tumor: synonymous with cancer.
  • Benign neoplasm or benign tumor: a tumor (solid neoplasm) that stops growing by itself, does not invade other tissues and does not form metastases.
• Invasive tumor is another synonym of cancer. The name refers to invasion of surrounding tissues.
• Pre-malignancy, pre-cancer or non-invasive tumor: A neoplasm that is not invasive but has the potential to progress to cancer (become invasive) if left untreated. These lesions are, in order of increasing potential for cancer, atypia, dysplasia and carcinoma in situ.

The following terms can be used to describe a cancer:

• Screening: a test done on healthy people to detect tumors before they become apparent. A mammogram is a screening test.
• Diagnosis: the confirmation of the cancerous nature of a tumor. This usually requires a biopsy or removal of the tumor by surgery, followed by examination by a pathologist.
• Surgical excision: the removal of a tumor by a surgeon.
  • Surgical margins: the evaluation by a pathologist of the edges of the tissue removed by the surgeon to determine if the tumor was removed completely ("negative margins") or if tumor was left behind ("positive margins").
• Grade: a number (usually on a scale of 3) established by a pathologist to describe the degree of resemblance of the tumor to the surrounding benign tissue.
• Stage: a number (usually on a scale of 4) established by the oncologist to describe the degree of invasion of the body by the tumor.
• Recurrence: new tumors that appear at the site of the original tumor after surgery.
• Metastasis: new tumors that appear far from the original tumor.
• Chemotherapy: treatment with drugs.
• Psychotherapy: individual or group treatment, directed at personal wellbeing, with regard to emotional, behavioral and existential issues.
• Radiation therapy: treatment with radiations.
• Adjuvant therapy: treatment, either chemotherapy or radiation therapy, given after surgery to kill the remaining cancer cells.
• Neoadjuvant therapy: treatment, either chemotherapy or radiation therapy, given before surgery to shrink the tumor.
• Prognosis: the probability of cure after the therapy. It is usually expressed as a probability of survival five years after diagnosis. Alternatively, it can be expressed as the number of years when 50% of the patients are still alive. Both numbers are derived from statistics accumulated with hundreds of similar patients to give a Kaplan-Meier curve.

Psycho-Oncology is a field that relates to the psychological aspects of cancer. This may involve psychological influences at the onset and during the course of the cancer, effects of psychotherapy on cancer growth or survival, or it may involve the quality of life and psychosocial issues relevant to cancer patients.

Classification

Tumours are usually classified by their anatomical location. They can also be classified by the normal tissue the resemble most. The World Health Organization classifies tumours as such :

• Tumours of the Central Nervous System
• Tumours of Haematopoietic and Lymphoid Tissues
• Tumours of the Digestive System
• Tumours of the Breast and Female Genital Organs
• Tumours of Soft Tissue and Bone
• Skin Tumours
• Tumours of the Urinary System and Male Genital Organs
• Tumours of Endocrine Organs
• Head and Neck Tumours
• Tumours of the Lung, Pleura, Thymus and Heart

Related Videos

Gregory Hannon, Molecular Biologist at Cold Spring Harbor Laboratory, explores the use of RNA interference (RNAi) as a gene manipulation tool that may revolutionize cancer treatment, in this video from BigThink:

Iain Couzin, Professor of Ecology & Evolutionary Biology at Princeton University, discusses small and large-scale biological collectives, and how this cutting-edge research promises to deepen our understanding of cancer:

This video introduces an NIH study that examined the link between exercise and cancer risk, paying special attention to whether or not getting adequate sleep further affects the risk of developing cancer.

References

1. ↑ Kiecolt-Glaser, J K et. al. "Distress and DNA repair in human lymphocytes." Journal of behavioral medicine 8 (1985): 311-20 - Abstract
2. ↑ Graves, P L, and L A Mead, and T A Pearson. "The Rorschach Interaction Scale as a potential predictor of cancer." Psychosomatic medicine 48: 549-63 - Abstract
3. ↑ Shaffer, J W et. al. "Clustering of personality traits in youth and the subsequent development of cancer among physicians." Journal of behavioral medicine 10 (1987): 441-7 - Abstract
4. ↑ Thomas, C B. "Precursors of premature disease and death. The predictive potential of habits and family attitudes." Annals of internal medicine 85 (1976): 653-8 - Abstract
5. ↑ Thomas, C B, and K R Duszynski, and J W Shaffer. "Family attitudes reported in youth as potential predictors of cancer." Psychosomatic medicine 41 (1979): 287-302 - Abstract
6. ↑ http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1465423&blobtype=pdf
7. ↑ Challis, G B, and H J Stam. "The spontaneous regression of cancer. A review of cases from 1900 to 1987." Acta oncologica (Stockholm, Sweden) 29 (1990): 545-50 - Abstract
8. ↑ Zahl, Per-Henrik, and Bjørn Heine Strand, and Jan Maehlen. "Incidence of breast cancer in Norway and Sweden during introduction of nationwide screening: prospective cohort study." BMJ (Clinical research ed.) 328 (2004): 921-4 - Abstract