General oncology

Last updated: November 3, 2023

Summarytoggle arrow icon

Oncology is the science of tumors. This article explains basic concepts relevant to the development, progression, spread, and diagnosis of cancer. Histological analysis helps to determine tumor type and grade, whereas the TNM classification system is used to assess staging. Because it is standardized and used internationally, the TNM classification helps unify oncological research and therapy protocols. Metastasis occurs via different pathways mainly by hematogenous or lymphatic spreading.

Principles of cancer care, paraneoplastic syndromes, and tumor markers are covered in detail in their respective articles.

Nomenclaturetoggle arrow icon


Basic terminology in oncology
Term Definition
Normal cell
  • Abnormal growth of cells or edema that leads to swelling of tissue
  • Tumor does not necessarily mean neoplasia.


  • A benign mass composed of mature cells that are native to the tissue of origin but have abnormal tissue organization (e.g., Peutz-Jeghers syndrome, pulmonary hamartoma, iris hamartoma)
  • Low potential to undergo malignant transformation
  • Presence of normal tissue at a site where this type of tissue is not normally found (e.g., the presence of gastric tissue in the ileum, as is sometimes seen in Meckel diverticulum)
Carcinoma in situ (CIS)
Invasive carcinoma
  • Spread of malignant cells to distant organs, tissues (e.g., colorectal cancer spreading to the liver)
    • Lymphatic spread
    • Hematogenous spread

Benign and malignant tumors

Overview of benign and malignant tumors
Benign tumor Malignant tumor
Differentiation (grading)
  • Well-differentiated (low grade)
  • Poorly differentiated (high grade)
  • Slow growth with a low rate of cell division (low mitotic rate)
  • Mass effect with compression of non-tumor tissue
  • Unpredictable growth, high rate of cell division (high mitotic rate)
  • Suppressed cellular apoptosis
  • Locally destructive and invasive
  • Necrosis is rare.
  • Well-demarcated from surrounding tissue
  • Almost no irregularities of cellular structures
  • Detection and confirmation of cellular atypia

Metastasis and relapse

Tumor origin

Types of tumors based on cell origin
Type of tumors Cell origin Benign tumor Malignant tumor
Epithelial tumors
  • Papilloma

Mesenchymal tumors

  • Fibrosarcoma
  • Lymphatic vessels
  • N/A
Special variants of mesenchymal tumors
  • N/A
  • N/A
Neuroectodermal tumors
Germ cell tumors
  • Germ cells
Embryonal tumors
  • N/A

General epidemiologytoggle arrow icon

In 2020, approximately 1.8 million people will be diagnosed with cancer in the United States. Cancer is the 2nd leading cause of death; after heart disease. The most common type of cancer in both men and women is skin cancer, with basal cell carcinoma being more common than squamous cell carcinoma and melanoma. [1]

Epidemiology of common cancer types in 2020 [2]

The following numbers are an estimation of new cancer cases and their mortality in the United States (excluding skin cancer ).

Epidemiology of most common cancer types


Incidence/year in men Incidence/year in women Mortality/year
Breast cancer 2,620 276,480 42,690
Lung and bronchus cancer 116,300 112,520 135,720
Prostate cancer 191,930 N/A 33,330
Colorectal cancer 78,300 69,650 53,200
Bladder cancer 62,100 19,300 17,980
Kidney cancer 45,520 28,230 14,830
Uterine cancer N/A 65,620 12,590
Pancreatic cancer 30,400 27,200 47,050
Thyroid cancer 12,720 40,170 2,180
Non-Hodgkin lymphoma 42,380 34,860 19,940
Leukemia 35,470 25,060 23,100

Carcinogenesistoggle arrow icon


  • Definition: a multistep process by which normal cells develop and accumulate genetic mutations (inherited or acquired), resulting in a monoclonal expansion of mutated cells that can progress to the development of neoplasia
  • Process
    1. Initiation: DNA damage
    2. Promotion: DNA damage passed on
    3. Latency: the time between promotion and progression
    4. Progression: proliferation of the neoplastic cell line with the acquired DNA damage, leading to malignant transformation

Properties of malignant cells

Defense mechanisms of malignant cells [7]

Oncogenetoggle arrow icon

Adenocarcinoma of Lung Kinase”: Cancer (adenocarcinoma of lung) and the gene product (tyrosine kinase) are associated with ALK mutations.

L-myc is associated with lung cancer and n-myc with neuroblastoma.

c-KIT mutations affect CytoKIne recepTor production.

BCL-2 mutations are associated with diffuse large B-cell lymphoma.

Tumor suppressor genestoggle arrow icon

  • Tumor suppressor gene: a gene that normally controls and suppresses cell proliferation
    • Loss of function or inactivation leads to an increased risk of developing cancer.
    • Both alleles must be mutated in order for complete loss of function of the gene.
Overview of tumor suppressor genes
Gene Chromosome Gene product Associated malignancy
  • 17p13.1
  • 13q14.2
  • 9p21.3

APC gene
  • 5q22.2

PTEN [13]

  • 10q23
  • Negatively regulates the PI3k/AKT pathway
  • 17q21.31
  • 13q13.1
MMR gene family
  • Varies depending on the mutated protein
DCC (Deleted in colorectal cancer)
  • 18q21.2

SMAD4 (DPC4) (Deleted in pancreatic cancer)
  • 18q21.2
  • 11q13.1
  • 17q11.2

  • 22q12.2

  • Merlin (schwannomin)
TSC1 (Tuberous sclerosis complex 1)
  • 9q34.13
TSC2 (Tuberous sclerosis complex 2)
  • 16p13.3
  • 3p25.3
WT1 (Wilms Tumor 1)
  • 11p13
WT2 (Wilms Tumor 2)
  • 11p15.5

Mutations of the Rb (retinoblastoma) gene mutations cause Retinoblastomas and bone cancer (osteosarcoma).

PTEN mutation is associated with cancers of the Prostate, breasT, and ENdometrium.

Mutations in MEN 1 affect its gene product: MENin.

Carcinogenstoggle arrow icon

Chemical carcinogens

Examples of chemical carcinogens
Substance Sources of exposure Malignancy
Alkylating agents
Aromatic amines (β-naphthylamine, benzidine)
  • Contaminated groundwater (esp. in developing countries)
  • Pesticides, herbicides (e.g., vineyard workers)
  • Metal smelting
  • Insulation material (formerly used in construction and shipbuilding)
  • Asbestos cement (fibrolite), roofing, and siding
Benzene, benzol
  • Occupations that involve beryllium production and processing, esp.: [14][15]
    • Smelting and founding
    • Welding
    • Manufacturing
      • Industrial ceramics
      • Electronics
      • Automotive, aerospace, and defense components
      • Dental supplies and prostheses
  • See also “Beryllium” in “Rare pneumoconioses”.
  • Significant in workers exposed to:
    • Galvanization (chrome plating)
    • Paint and glass manufacturing
    • Tanning leather
    • Building materials
Cigarette smoke
  • First-hand smoke: smoke inhaled by the smoker
  • Second-hand smoke: exhaled smoke that is inhaled by others in the vicinity of the smoker
  • Third-hand smoke: smoke particles that adhere to surfaces in the surroundings of the smoker
  • All three have been proven to be carcinogenic.
  • Alcoholic beverages
  • Occupations that involve mining, smelting, welding, and casting of alloys (e.g., in coins, jewelry)
  • Cured meats (e.g. bacon) and fish
  • Cold-smoked foods
  • Tobacco [16]
  • Accumulation in basements
  • Uranium mining (extraction of uranium ore from the ground): miners are exposed to radon gas, which is emitted during natural radioactive decay of uranium ore
  • Occupations that involve cutting, drilling, chipping, or grinding crystalline silica (e.g., quartz) or materials that contain it (e.g., sand, granite), esp.: [18]
    • Sandblasting
    • Glass manufacturing
    • Construction work
  • See also “Etiology” in “Silicosis.”

Vinyl chloride

Wood dust
  • Woodworking (e.g., sawing, drilling, sanding)


Overview of radiation
Type Occurrence Malignancy
Nonionizing radiation
  • UV-B
Ionizing radiation

Oncogenic infections

Cancer-Immunity cycletoggle arrow icon

Grading and stagingtoggle arrow icon

Tumor grading

  • Definition: the process of classifying tumors based on their histological appearance (degree of cell differentiation)
  • Indicators of poor differentiation
  • Anaplasia: loss of morphological features of malignant cells so that resemblance to normal cells of a particular tissue where tumor cell originated from is lost

Grading systems

  • AJCC grading system
    • Most commonly used grading system for nonhematological malignancies
    • Can be applied to a wide range of tumors
    • Usually, higher-grade tumors are more aggressive than lower-grade tumors.
Grading Differentiation of malignant tissue
G1 Well differentiated (low grade)
G2 Moderately differentiated (intermediate grade)
G3 Poorly differentiated (high grade)
G4 Undifferentiated/anaplastic (high grade)
GX Differentiation cannot be assessed.

Tumor staging [19]

  • Definition: a method of determining and classifying a tumor according to its spread throughout the body
  • Prognosis: The stage of the tumor is typically more important than the grade in determining the prognosis.

Spread determines Stage, and Stage determines Survival more than grade.

TNM classification

  • T stage: size or direct extent of the primary tumor
  • N stage: involvement of regional lymph nodes
  • M stage: presence of distant metastasis
  • By adding a "C" to any category, it is possible to express the certainty of the diagnosis:
  • By adding a prefix to TNM it is possible to indicate additional diagnostic or clinical information:
    • cTNM: staging based on clinical criteria
    • pTNM: histopathological staging

T, N, and M have independent prognostic values. N and M are typically the most important determinants of prognosis.

AJCC staging system

  • Stage 0 (carcinoma-in-situ)
  • Stage I–III: Tumor spread into nearby tissues.
  • Stage IV: Tumor spread to distant parts of the body.

Cancer-specific staging systems

Metastasistoggle arrow icon


  • Metastasis: the spread of malignant cells to distant organs, tissues (e.g., colorectal cancer spreads to the liver)

Types of metastasis [20]

Four Carcinomas Route Hematogenously”: Follicular thyroid carcinoma, Choriocarcinoma, Renal cell carcinoma, and Hepatocellular carcinoma spread via the blood, compared to most carcinomas which spread lymphatically.

Mechanisms of metastasis

Common sites for cancer metastasis [25]

Common origins of cancer metastases
Organ with metastasis

Associated features

Primary tumor location
  • Approximately 50% of brain tumors result from metastases.
  • Appear in the white-gray matter junction as multiple well-circumscribed lesions

Approximately 50% of brain tumors and most bone tumors are not primary tumors but rather result from metastases.

Cancers spread progressively to the liver”: Colon, Stomach, and Pancreas cancers metastasize to the liver.

BLT with a kosher pickle and mayo on the bun”: Breast, Lung, Thyroid, Kidney, Prostate cancers, and Multiple myeloma metastasize to the bone.

Tumor markerstoggle arrow icon

Definition: Substances produced by cancer cells that are found in increased amount in the bloodstream, urine, or body tissues.

For more details for each tumor marker see the article on tumor markers.

Conditions associated with tumorstoggle arrow icon

Neurocutaneous syndromes associated with neoplasms

Premalignant mucocutaneous conditions

Overview of premalignant mucocutaneous conditions
Condition Key features Neoplasms
Actinic keratosis
  • Small lesion with sandpaper-like texture
  • Lesions grow and become brown or erythematous and scaly
Bowen disease
  • Erythematous and scaly
  • Irregularly shaped with sharply defined borders
  • Persistent white plaques that usually cannot be scraped off (predominantly affects oral cavity)
Erythroplasia of Queyrat
  • Single or multiple sharply demarcated, non-healing lesions
  • Ulcerate and bleed easily
Lentigo maligna
  • Darkly pigmented macule with irregular borders on sun exposed skin
  • Gradual growth, color irregularities, surrounding "island-like" speckling
Dysplastic nevi
Xeroderma pigmentosum

Gastrointestinal conditions associated with neoplasms

Overview of gastrointestinal conditions associated with neoplasms
Condition Key features Neoplasms
Inflammatory bowel disease Ulcerative colitis
Crohn disease
Plummer-Vinson syndrome
Barrett esophagus
Atrophic gastritis Autoimmune metaplastic atrophic gastritis (AMAG)
Environmental metaplastic atrophic gastritis (EMAG)
Liver cirrhosis

Infectious conditions associated with neoplasms

Overview of infectious conditions associated with neoplasms
Condition Key features Neoplasms
DNA virus infections EBV infection
HBV infection
HHV-8 infection
  • Infects endothelial cells causing malignant, multifocal, highly vascularized tumors
HPV 16
HPV 18
RNA virus infections HTLV-1 infection
HIV infection
HCV infection
Nonviral pathogen infections Schistosoma haematobium
Clonorchis sinensis (Chinese liver fluke)
Streptococcus bovis
Clostridium septicum

Miscellaneous conditions associated with neoplasms

Miscellaneous conditions associated with neoplasms
Condition Key features Neoplasms
Down syndrome
Paget disease of the bone

Paraneoplastic conditions

Overview of paraneoplastic conditions
Condition Key features Neoplasms
Neuromuscular Lambert-Eaton myasthenic syndrome
Myasthenia gravis
  • Proximal muscle weakness affecting both sides
Neurological Paraneoplastic encephalomyelitis
  • Immune reaction against neural antigens
Paraneoplastic cerebellar degeneration
Opsoclonus-myoclonus syndrome
Endocrine Cushing syndrome
Syndrome of inappropriate ADH secretion
Hypercalcemia of malignancy
Mucocutaneous Malignant acanthosis nigricans
Necrolytic migratory erythema
  • Multiple areas of centrifugally spreading erythema that develop into develop into painful and pruritic crusty patches with central areas of bronze-colored induration
Paraneoplastic seborrheic keratosis (Leser-Trélat sign)
Skeletal Hypertrophic pulmonary osteoarthropathy (Bamberger-Marie syndrome)
  • Ectopically produced growth factors (e.g., VEGF, PDG) → clubbing, joint pain, thickening of tubular bones
Hematological Polycythemia
Pure red cell aplasia
  • Absence of red cell precursor cells → anemia
Good syndrome
Trousseau syndrome (thrombophlebitis migrans)
Nonbacterial thrombotic endocarditis

Neoplastic fever

  • Most cancers

Membranous glomerulonephritis

Referencestoggle arrow icon

  1. Cell Signaling in Cancer. Updated: December 17, 2018. Accessed: March 6, 2020.
  2. Bhagwat AS, Vakoc CR. Targeting Transcription Factors in Cancer. Trends in Cancer. 2015; 1 (1): p.53-65.doi: 10.1016/j.trecan.2015.07.001 . | Open in Read by QxMD
  3. Mendonsa AM, Na T-Y, Gumbiner BM. E-cadherin in contact inhibition and cancer. Oncogene. 2018; 37 (35): p.4769-4780.doi: 10.1038/s41388-018-0304-2 . | Open in Read by QxMD
  4. Liberti MV, Locasale JW. The Warburg Effect: How Does it Benefit Cancer Cells?. Trends Biochem Sci. 2016; 41 (3): p.211-218.doi: 10.1016/j.tibs.2015.12.001 . | Open in Read by QxMD
  5. Rabinovich GA, Gabrilovich D, Sotomayor EM. Immunosuppressive Strategies that are Mediated by Tumor Cells. Annu Rev Immunol. 2007; 25 (1): p.267-296.doi: 10.1146/annurev.immunol.25.022106.141609 . | Open in Read by QxMD
  6. Buchbinder EI, Desai A. CTLA-4 and PD-1 Pathways: Similarities, Differences, and Implications of Their Inhibition.. Am J Clin Oncol. 2016; 39 (1): p.98-106.doi: 10.1097/COC.0000000000000239 . | Open in Read by QxMD
  7. Flynn SD, Murren JR, Kirby WM, Honig J, Kan L, Kinder BK. P-glycoprotein expression and multidrug resistance in adrenocortical carcinoma.. Surgery. 1992; 112 (6): p.981-6.
  8. Cooper R, Harrison A. The uses and adverse effects of beryllium on health. Indian Journal of Occupational and Environmental Medicine. 2009; 13 (2): p.65.doi: 10.4103/0019-5278.55122 . | Open in Read by QxMD
  9. Beryllium Toxicity. . Accessed: December 17, 2020.
  10. Hecht SS, Hoffmann D. Tobacco-specific nitrosamines, an important group of carcinogens in tobacco and tobacco smoke. Carcinogenesis. 1988; 9 (6): p.875-884.doi: 10.1093/carcin/9.6.875 . | Open in Read by QxMD
  11. What Causes Lung Cancer. Updated: November 24, 2017. Accessed: March 6, 2020.
  12. Deslauriers JR, Redlich CA. Silica Exposure, Silicosis, and the New Occupational Safety and Health Administration Silica Standard. What Pulmonologists Need to Know.. Annals of the American Thoracic Society. 2018; 15 (12): p.1391-1392.doi: 10.1513/AnnalsATS.201809-589ED . | Open in Read by QxMD
  13. Cowherd SM. Tumor Staging and Grading: A Primer. Humana Press ; 2011: p. 1-18
  14. Kumar V, Abbas AK, Aster JC. Robbins & Cotran Pathologic Basis of Disease. Elsevier Saunders ; 2014
  15. Yu X, Wang P, Liang Z. Cavitary Pulmonary Metastases: CT Features and Their Correlation with the Pathology of the Primary Malignancy. The Chinese-German Journal of Clinical Oncology. 2004; 3 (1).doi: 10.1007/s10330-004-0208-1 . | Open in Read by QxMD
  16. Gunasekaran K, Baskaran B, Rahi MS, Rudolph D, Parekh J. Cavitating pulmonary metastases from a renal cell carcinoma. Clinics and Practice. 2020; 10 (1).doi: 10.4081/cp.2020.1234 . | Open in Read by QxMD
  17. Sagar D, Adeni A. Unusual cystic lung metastasis. BMJ Case Reports. 2018: p.bcr-2018-224648.doi: 10.1136/bcr-2018-224648 . | Open in Read by QxMD
  18. Fielli M, Avila F, Saino A, Seimah D, Fernández Casares M. Diffuse cystic lung disease due to pulmonary metastasis of colorectal carcinoma. Respiratory Medicine Case Reports. 2016; 17: p.83-85.doi: 10.1016/j.rmcr.2015.12.006 . | Open in Read by QxMD
  19. Obenauf AC, Massagué J. Surviving at a Distance: Organ-Specific Metastasis. Trends in Cancer. 2015; 1 (1): p.76-91.doi: 10.1016/j.trecan.2015.07.009 . | Open in Read by QxMD
  20. Lodish HF, Zipursky HF, Matsudaria HF, et al.. Molecular Cell Biology. Scientific American Library ; 2000
  21. Assi T, Kattan J, Rassy E, et al. Targeting CDK4 (cyclin-dependent kinase) amplification in liposarcoma: A comprehensive review. Crit Rev Oncol Hematol. 2020; 153: p.103029.doi: 10.1016/j.critrevonc.2020.103029 . | Open in Read by QxMD
  22. Lee B, McArthur GA. CDK4 inhibitors an emerging strategy for the treatment of melanoma. Melanoma Management. 2015; 2 (3): p.255-266.doi: 10.2217/mmt.15.14 . | Open in Read by QxMD
  23. Coleman WB. Molecular Pathogenesis of Prostate Cancer. Elsevier ; 2018: p. 555-568
  24. Skin Cancer. . Accessed: December 17, 2020.
  25. Cancer Stat Facts: Common Cancer Sites. Updated: April 1, 2018. Accessed: June 18, 2018.
  26. Chen C-Y, Peng H-C, Chen Y-Y, Chan C-C, Yu C-J. Association of environmental heavy metals exposure and lung cancer incidence and prognosis. 11.1 Lung Cancer. 2016.doi: 10.1183/13993003.congress-2016.pa2805 . | Open in Read by QxMD

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