This is the basic concept of tumors or neoplasms

Definition

According to the WHO statistics of 2021, cancer is among the top 10 leading causes of death globally. Despite current advancement in healthcare research and treatment, it’s still a tremendous burden among patients and their relatives. Along with its morbidity and mortality, its infliction of psychological stress, financial strain and pain among sufferers shouldn’t be overlooked.

Neoplasm or tumor is the abnormal mass of tissue, whose growth exceeds adjacent normal tissues even when causative stimuli stop. Any genetic mutations in the parent tumor cells are transferable to the daughter cells. In this way, daughter tumor cells are able to grow and proliferate independently due to gene mutation. Tumor cells can be benign and malignant.

Benign tumors are localized, noninvasive tumors that can be removed surgically. Malignant tumors are cancers that invade neighboring tissues and can spread to distant sites to cause death.

Benign tumors of mesenchymal origin have the suffix-oma attached to the cell of origin.

Tumors of epithelial, parenchymal origin are classified as: adenoma (glandular epithelial cell origin); papilloma (small or large finger-like or warty projection of epithelial cells); cystadenoma (large cystic glandular epithelial mass): papillary cystadenoma (papillary projection into cystic space); polyp (large visible mass).

Below are examples of benign mesenchymal tumors:

1. Fibroma
2. Chondroma
3. Osteoma
4. Lipoma
5. Hemangioma
6. Lymphangioma
7. Meningioma
8. Leiomyoma
9. Rhabdomyoma

Examples of benign epithelial tumors:

1. Squamous cell papilloma
2. Adenoma; papilloma; cystadenoma (for epithelia of glands and ducts)
3. Bronchial adenoma
4. Renal tubular adenoma
5. Nevus (melanocyte)
6. Liver cell adenoma
7. Transitional-cell papilloma (renal pelvis, ureter, bladder, urethra)
8. Hydatidiform mole (trophoblast)

Malignant tumors of mesenchymal origin are usually called sarcomas (fleshy). Epithelial origin may be: carcinomas; mixed tumors (tumors of 2 cell lineages from same monoclonal parent); Teratomas

Carcinomas are divided into: Squamous cell carcinoma (squamous epithelial cell-like tumor); adenocarcinoma (glandular epithelial cell-like tumor).

Below are examples of malignant mesenchymal tumors:

1. Fibrosarcoma
2. Chondrosarcoma
3. Osteosarcoma
4. Liposarcoma
5. Angiosarcoma
6. Lymphangiosarcoma
7. Invasive meningioma
8. Leiomyosarcoma
9. Rhabdomyosarcoma

Examples of malignant epithelial tumors:

1. Squamous cell carcinoma
2. Adenocarcinoma; papillary carcinoma; cystadenocarcinoma (epithelia of glands, ducts)
3. Bronchogenic carcinoma
4. Renal cell carcinoma
5. Malignant melanoma (melanocyte)
6. Hepatocellular carcinoma
7. Transitional-cell carcinoma (renal pelvis, ureter, bladder, urethra)
8. Choriocarcinoma (trophoblast)
9. Seminoma; embryonal carcinoma (testicular origin)

Other examples include:

1. Pleomorphic adenoma (mixed benign tumor of salivary gland)
2. Malignant mixed tumor of salivary gland
3. Nephroblastoma (malignant renal tumor)
4. Teratomas

Next, we shall consider the characteristics of a benign and malignant tumor. In order to better differentiate both benign and malignant neoplasms, the followings are assessed: differentiation and anaplasia; rate of growth; local invasion; metaplasia.

Differentiation and anaplasia

Differentiation refers to the extent a tumor cell resembles its neighboring normal parenchymal tissue functionally and morphologically. Anaplasia refers to the lack of differentiation, and is the main feature of malignancy.  

Bening tumor cells have well differentiated cells, comparably fewer mitoses and normal arrangement. Malignant cells may range from well differentiated to undifferentiated.

In well differentiated cells, daughter cells derived from parent cells have the capacity to differentiate. However, this is not the case with poorly differentiated cells as this capacity is lost.

Malignant tumors that are poorly differentiated are anaplastic. Undifferentiated malignant tumors possess the following features: abnormal size and shape of cell and nuclei; extra large nuclei with dark staining property due to hyperchromatin; highly dividing cells; poor arrangement of tumor cells; large central area of ischemic necrosis; 2 or more large hyperchromatic nuclei.

Carcinoma in situ is a preinvasive tumor in which severe dysplastic epithelial cells are limited to basal membrane. Dysplasia is the abnormal size, shape, and framework of epithelial cells. This phenomenon usually occurs in metaplasia. Other than its pleomorphic property, it may be highly proliferative and contains hyperchromatic nuclei. Dysplastic changes are seen in Barett esophagus and long-term smokers.

Rate of growth

The length of cell cycle, number of cells replicating and number of cells that die all determine the rate of tumor growth. Tumor cells usually have an equal or longer cell cycle than comparable normal cells. Consequently, this may lead to more or fewer cells replicating than dying, or differentiating.

Fast growing tumors leave the cell cycle sooner, hence why some anti-cancer therapies won’t work just alone. In comparison with benign tumors, malignant tumors grow more rapidly.    

Local Invasion

Benign tumors don’t invade nearby tissues. A fibrous capsule covers a benign tumor which makes them separable, mobile, palpable with well defined border.   

Malignant tumors infiltrate, invade and destroy surrounding tissues. They have a poorly defined border which makes surgical resection difficult.

Metastasis

Metastasis is the spread of tumor of primary origin to a distant site. This feature clearly defines a malignant tumor. All malignant tumors metastasize except basal cell carcinoma of the skin, and gliomas that rarely metastasize. The chances of cure reduce when tumor cells metastasize.