Next Lesson - Pathogenesis of Neoplasms
Core
Any nucleated cell (a cell with a nucleus) has the potential to form a neoplasm. A neoplasm is an abnormal growth of cells that persists after the stimulus (the trigger that started it) is removed. This happens through accumulation of genetic alterations that change the appearance and behaviour of the cell. Tumours are any clinically detectable lump or swelling, and can be defined as either neoplastic or non-neoplastic.
Neoplasms are classified according to how they behave and their morphology (how the cells and tissue look). Broadly they can be classified into benign and malignant. Malignant neoplasms are commonly known as cancers.
Benign neoplasms are non-invasive and remain confined to their site of origin. They are often well circumscribed (sharply defined) and may be encapsulated (enclosed in a thin layer of connective tissue). They have a pushing outer margin (the edge presses against nearby tissue rather than invading it). Under the microscope the cells are typically well differentiated and resemble the tissue they come from.
Diagram - The growth of a benign neoplasm. It is regular and well circumscribed
SimpleMed original by Dr. Emily Smith
Image - A benign neoplasm under the microscope. The cells look uniform, with round nuclei of similar size, and still resemble the original tissue
Creative commons source by No machine-readable author provided. KGH assumed (based on copyright claims). [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]
Malignant neoplasms are defined by their ability to invade surrounding tissues and spread to different sites (metastasise). They often grow more rapidly than benign tumours and may have irregular edges with no clear margin. This type of neoplasm often has central necrosis due to inadequate perfusion when it outgrows its blood supply.
The degree of differentiation varies between malignant tumours. Well-differentiated cancers retain features of their tissue of origin; poorly differentiated tumours may show little resemblance. Atypical nuclei (abnormal-looking nuclei) may show enlargement, hyperchromasia (dark staining), chromatin clumping and variation in size and shape (pleomorphism). Increased or abnormal mitotic figures (cells caught in the middle of dividing) can also be present. These findings support diagnosis but are not universal features of every cancer.
Diagram - The growth of a malignant neoplasm. It is invading into the surrounding tissues, giving it an irregular edge. The tumour is growing fast, resulting in ulceration and areas of necrosis
SimpleMed original by Dr. Emily Smith
Image - A malignant peripheral nerve sheath tumour (a cancer arising from the covering of a peripheral nerve) under the microscope. This example illustrates abnormal spindle-cell (long, thin, tapered) morphology; malignant tumours vary in their resemblance to normal tissue.
Creative commons source by Nephron [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]
Table - Differences between benign and malignant neoplasms
SimpleMed original by Dr. Emily Smith
Nomenclature of Tumours (Tumour naming)
The naming of tumours often depends on the origin tissue, and whether the tumour is benign or malignant.
Epithelial Tumours
- Benign Tumours
- Benign tumours of epithelium are classified as either a papilloma or an adenoma, and the name also includes the tissue or cell type they originate from.
- A papilloma is a benign tumour of non-glandular epithelium (epithelium that does not form glands). Its name starts with the cell type, e.g. stratified squamous papilloma (a papilloma of flat cells arranged in layers).
- An adenoma is a benign tumour of glandular epithelium e.g. colonic adenomas.
- Malignant Tumours
- A malignant tumour of epithelium is called a carcinoma, prefixed by the cell type e.g. squamous cell carcinoma.
- A malignant tumour of glandular epithelium is called an adenocarcinoma (a type of carcinoma), e.g. colonic adenocarcinoma.
Connective Tissue Tumours
- These tumours have a prefix associated with each tissue as shown in the table below, for example cartilage has the prefix ‘chondro-’.
- Benign
- This type of tumour has the suffix ‘-oma’.
- Malignant
- This type of tumour has the suffix ‘-sarcoma’.
Table - Nomenclature of benign and malignant tumours
SimpleMed original by Dr. Emily Smith
Despite these rules of nomenclature, some tumours do not follow them. For example, lymphoma and melanoma end in ‘-oma’ but are malignant. Many tumours are also named after a person (an eponym), as in the examples below.
- Burkitt’s lymphoma: a type of lymphoma that arises from B cells (a type of white blood cell)
- Hodgkin’s lymphoma: a lymphoma in which abnormal lymphocytes called Reed-Sternberg cells (usually formed from B cells) are found
- Ewing’s sarcoma: a malignant neoplasm that usually arises in bone, and sometimes in the soft tissue near bone
- Kaposi’s sarcoma: a malignant neoplasm of vascular endothelium (the lining of blood vessels)
In-situ and Invasive Carcinomas
A carcinoma in-situ is a collection of neoplastic epithelial cells that have not yet invaded through the basement membrane (the thin layer of tissue beneath the epithelium). It cannot access routes of metastasis such as lymphatics (vessels that carry lymph, a fluid drained from the tissues, towards the lymph nodes) and blood vessels. If a carcinoma in-situ is detected at this point (for example as part of a screening programme), it can often be completely removed (excised) before it becomes invasive.
An invasive carcinoma is one that has broken through the basement membrane. This means it can metastasise.
Diagram - The progression of cells from a normal state through to a malignant state
SimpleMed original by Dr. Emily Smith
Staging and Grading of Tumours
Staging and grading both help to predict the prognosis (the likely outcome). Staging describes how big a tumour is and how far it has spread, and grading describes how abnormal the tumour cells look. In general, a higher grade or stage means a worse prognosis.
Grading is used to estimate the behaviour of the malignancy from histological features (how the tissue looks under the microscope). Most tumours are graded from 1 to 3 or from 1 to 4, with 1 being well-differentiated (low grade) and the highest grade being poorly differentiated or undifferentiated (high grade). The grading system differs between types of cancer. Higher grade tumours tend to grow rapidly and spread faster than lower grade tumours.
Tumour grade is usually based on findings such as these (the more abnormal they look, the higher the grade):
- Degree of differentiation: how much the tumour resembles normal tissue
- Appearance of nuclei: size, hyperchromasia, pleomorphism
- Presence of mitoses
The stage of a tumour is determined by the size of the primary tumour, whether it has spread to nearby lymph nodes and whether it has spread to other organs (metastasis).
Staging involves assessment of the following, which together make up the TNM system (Tumour, Node, Metastasis):
- Tumour size
- Node involvement (spread to nearby lymph nodes)
- Metastasis to other organs
Diagram - TNM staging. For example, if a patient has a large primary tumour, local lymph node metastasis and no organ metastasis, their staging would be written as T3N1M0 (T3 is a large primary tumour, N1 is spread to nearby lymph nodes and M0 is no spread to other organs)
SimpleMed original by Dr. Emily Smith
The aim of cancer screening is to find disease at an early stage, or to find the people most at risk of it. Finding disease early lets treatment start early, which can make that treatment more likely to succeed.
In the UK there are screening programmes for cervical, breast and colorectal (bowel) cancer. In England, targeted lung cancer screening for current and former smokers aged 55 to 74 is also being rolled out, and is currently available only in some areas.
Cervical Cancer Screening
In England, everyone with a cervix (the neck of the womb) aged 25 to 64 should be offered cervical screening. The sample is tested first for high-risk human papillomavirus (HPV). If HPV is detected, the same sample is examined for cell changes that may require further assessment or treatment. Following a negative high-risk HPV result, routine invitations are every five years; abnormal results or relevant history may require earlier follow-up. Screening helps prevent cervical cancer by finding high-risk HPV and any early cell changes (precancerous changes, which could turn into cancer) so that they can be treated. The NHS is also introducing an HPV test that can be done at home, by invitation only, for people with a cervix aged 30 to 65 who have not had cervical screening after being invited in the past.
Breast Cancer Screening
In England, breast screening is routinely offered to women from the age of 50 up to their 71st birthday. The first invitation comes between the ages of 50 and 53, and invitations are then every three years. It involves having a mammogram, an x-ray of the breasts. A mammogram can detect changes such as asymmetrical densities (uneven areas of dense breast tissue) or calcifications (tiny calcium deposits) that may indicate cancer. Women with a possible abnormality are recalled (called back) for assessment. This can include more imaging and a core biopsy (a small sample of tissue taken through a hollow needle). Fine needle aspiration (drawing cells out through a thin needle) may be added in some services, but national guidance says that cytology (looking at individual cells under the microscope) should no longer be used alone to diagnose breast cancer before surgery.
Bowel Cancer Screening
In England, bowel cancer screening is routinely offered to people aged 50 to 74 every two years. A home faecal immunochemical test (FIT) is sent by post to check a stool sample for blood. A result requiring further investigation (blood found in the sample) leads to an appointment with a specialist nurse and usually a colonoscopy (a camera test of the bowel). Blood in the sample is a possible sign of bowel cancer, not a diagnosis of it.
Edited by:Dr. Bethany Turner
Reviewed by: Dr. Marcus Judge
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