Classifications

This section assumes knowledge from the sections: Basic biology, Cancer. 

Cancer can be classified differently and in different levels of depth depending on the context. This section will briefly outline a few different classifications of tumours.

Cancers can be separated into malignant or benign tumours. This is a largely unquantifiable term and is used more colloquially. Calling a tumour benign usually means it is not concerning, slow growing, unlikely to metastasize, or perhaps not even a cancer but a small lump caused by something other than genetic mutation. Malignant usually means it could metastasize, or is fast growing/aggressive and must be dealt with. These terms are nuanced and if confused or concerned about a personal case talk to your doctor. 

Cancers can be classified by the organ of origin, simply saying breast cancer, lung cancer, etc. However to go slightly more in depth cancers can be classified by the tissue of origin. Below is a list of some broad categories of tumour as separated by tissue.

Carcinoma: tumours originating from epithelial cells, meaning cells that make up the thin protective barriers lining most organs, internal passageways/cavities and the skin. There are many more ways of further differentiating around specific epithelial tissues, some common largely agreed upon categories are squamous cell carcinomas (referring to the top layer of the epidermis), basal cell carcinomas (referring to the bottom layer of the epidermis), and adenocarcinomas referring to epithelial glands such as the endometrium or goblet cells. (1)

Melanoma: tumours of the cells that produce pigments in places such as the eyes and skin. And is usually developed due to sunlight exposure. Melanomas can be further classified by their specific origin. (2)

Leukemia: cancers of the bone marrow in which the bone marrow is producing too many improper blood cells. There are 4 main types of leukemia; these broad categories fit most leukemia cases within them. Firstly there are myelogenous and lymphoblastic leukemias (4). Myelogenous effects red blood cells platelets and a specific type of white blood cell that matures into a subcategory of phagocytes called myeloblasts. Lymphoblastic leukemias refers to leukemia to do with specifically lymphocytes (3), the T and B cells discussed in the immune system section. Both myelogenous and lymphoblastic leukemia can be acute or chronic, this simply refers to the concentration of the mutated cancerous cells within the blood, acute being more than 20% and chronic being less than. Acute obviously having more intense symptoms than chronic, chronic usually needs faster medical attention than chronic, which can sometimes be monitored for an extended duration before clinical intervention is necessary (4). 

Lymphoma: blood cancer originating in the lymphatic system. Separated largely into hodgkins and non-hodgkins lymphoma. Hodgkin’s lymphoma is diagnosed by the presence of Reed Sternberg cells, (Non-Hodgkin’s lymphoma is then by contrast the lack of Reed Sternberg cells) which are abnormally large cells sometimes with 2 nucleases. There are a variety of other subtypes of lymphomas. (5) (6)

Myeloma: cancer of various plasma cells within the bone marrow replicating too much and abnormally usually spilling out into the bloodstream. Often called multiple myeloma as most patients have multiple sites the plasma cells have spread to. (7)

Sarcoma: cancer of connective tissues within the body such as muscle, bones, tendons etc. Generally these are separated into bone sarcomas, and soft tissue sarcomas meaning muscle, fat, etc. (8)

Brain neuroendocrine and germ cell tumours do not have larger defining categories for different tumours. These different tumour categories will be left to medical textbooks for now. 

Neuroendocrine tumours: a tumour of the system of nerves and glands used to produce and release hormones. This system normally works in processes such as digestion. (9)

Germ cell tumours: cancers of the cells that produce sex cells, sperm and egg. (10)

Brain tumours: cancer developed in brain tissue. It is rare for brain cancers to spread outside of the brain and are thus usually a localised problem. (11)

Cancers can also be classified by their difference to regular cells. By studying the cytology of cells it can give clues as to how certain cancers may develop or react. There are also grades for how different cells look compared to the normal cells. Cells that look close to normal could be grade 1 while vastly different cells could be grade 4. (12)

Lastly tumour stage is decided by the TNM system the Tumour size and type, the lymph Nodes it is present in, and whether it has Metastasized and where. This system is flexible and broad, and the rating can be adjusted based upon the available treatments and types of tumour. Generally there are 4 stages, below is a brief guide that aims to give a broad understanding of how the stages could be considered. (13)

Stage 1: localised and small.

Stage 2:  larger but still usually localised or being only present in local lymph nodes.

Stage 3: has grown into surrounding tissues and has spread to nearby lymph nodes.

Stage 4: the cancer has metastasized to different organs or distant parts of the body.

(14)

1.	Basal and Squamous Cell Carcinoma | Non-melanoma Skin Cancer | Cancer Council Australia | Cancer Council Australia. Cancer Council Australia. Published 2026. Accessed July 11, 2026. https://www.cancer.org.au/types-of-cancer/non-melanoma-skin-cancer
2.	Mayo Clinic. Melanoma – Symptoms and Causes. Mayo Clinic. Published December 30, 2023. Accessed July 11, 2026. https://www.mayoclinic.org/diseases-conditions/melanoma/symptoms-causes/syc-20374884
3.	Martin L. AML vs. ALL: Differences in symptoms, diagnosis, and survival. www.medicalnewstoday.com. Published September 24, 2021. Accessed July 11, 2026. https://www.medicalnewstoday.com/articles/aml-vs-all#differences
4.	Chennamadhavuni A, Lyengar V, Mukkamalla SKR, Shimanovsky A. Leukemia. PubMed. Published January 17, 2023. Accessed July 11, 2026. https://www.ncbi.nlm.nih.gov/books/NBK560490/
5.	Cleveland Clinic. Lymphoma. Cleveland Clinic. Published June 9, 2023. Accessed July 11, 2026. https://my.clevelandclinic.org/health/diseases/22225-lymphoma
6.	Lymphoma | Cancer Council Australia | Cancer Council Australia. Cancer Council Australia. Published 2026. Accessed July 11, 2026. https://www.cancer.org.au/types-of-cancer/lymphoma
7.	Myeloma | Cancer Council Australia. Cancer Council Australia. Published 2026. Accessed July 11, 2026. https://www.cancer.org.au/types-of-cancer/myeloma
8.	Sarcoma. Hudson Institute of Medical Research. Published December 3, 2024. Accessed July 11, 2026. https://hudson.org.au/disease/cancer/sarcoma/
9.	Neuroendocrine Tumours | Cancer Council Australia | Cancer Council Australia. Cancer Council Australia. Published 2026. Accessed July 11, 2026. https://www.cancer.org.au/types-of-cancer/rare-cancers/neuroendocrine-tumours
10.	Germ cell tumours. Cancer Australia. Published 2023. Accessed July 11, 2026. https://www.canceraustralia.gov.au/cancer-types/childrens-cancer/types-childrens-cancer/germ-cell-tumours
11.	Brain Tumor Types. www.hopkinsmedicine.org. Accessed July 11, 2026. https://www.hopkinsmedicine.org/health/conditions-and-diseases/brain-tumor/brain-tumor-types
12.	National Cancer Institute. Tumor Grade – NCI. www.cancer.gov. Published August 1, 2022. Accessed July 11, 2026. https://www.cancer.gov/about-cancer/diagnosis-staging/diagnosis/tumor-grade
13.	Cleveland Clinic. Cancer Staging System: What Do Stages and Grades Mean? Cleveland Clinic. Published 2022. Accessed July 11, 2026. https://my.clevelandclinic.org/health/diagnostics/22607-cancer-stages-grades-system
14.	Carbone A. Cancer Classification at the Crossroads. Cancers. 2020;12(4):980. doi:10.3390/cancers12040980