24 Neoplasms – Benign and Malignant

What is a Neoplasm?

The term neoplasm originates from the words ‘neo’ meaning new and ‘plasma’ which is Greek for formation. Within humans neoplasm refers to a new growth, or an abnormal mass of cells  that are not responding to normal genetic controls, reproducing excessively and possibly depriving nearby cells of nutrition.  This exuberant growth is characterized by cells that continue to divide (i.e. proliferate or go through mitosis) without the need for them to do so.  This mass of cells or neoplasm can be called a tumor and it may be malignant (cancerous) and it may be benign (non-cancerous).  Typically the cells are investigated using different laboratory tests including viewing their appearance under a microscope.  In this way it is often possible to identify the origin cell type (e.g. thyroid, lung, bone, etc.).  The appeance of the cells under the microscope, their morphology (shape, size of nuclei, etc.) can also be indicative of whether cells are pre-cancerour or cancerous.

Tumors are categorized as Benign or Malignant

In order to determine the best treatment, it is necessary to assess the tumor (neoplasm) to determine whether the mass of cells is potentially harmful or not.  There are some characterisitics that are typical of benign tumors and some characteristics that are observed when the tumor is cancerous (or malignant).

Benign Tumors

Benign tumors are typically slow-growing, encapsulated, and freely movable on palpation.  Benign tumors don’t metastasize and are therefore not considered cancerous.  The morphology of cells is similar to normal cells and is still considered differentiated (mature).   Cells in benign tumors usually have a normal number of chromosomes. The rates of mitosis are fairly normal and the mass grows slowly.  Benign tumors rarely cause systemic effects.  Additionally, once benign tumors are removed, they don’t usually recur.  Any damage to the body, typically is limited to surrounding tissue that may be compressed (e.g. blood vessels, esophagus).  However, benign tumors can be fatal in the brain due to the increase in intracranial pressure that can arise which leads less cranial blood flow, hypoxia and neuronal death.

There is a naming pattern for benign tumors, in that the suffix -oma is frequently used (e.g. adenoma = benign tumor comprised of epithelial glandular cells).  There are some exceptions to this rule, in the glioma is a malignant tumor consisting of cancerous neuroglial cells, and lymphoma is cancer of the lymphocytes.

Malignant Tumors

Malignant tumors on the other hand, lack a capsule, invade surrounding tissues, and are characterized by atypical, immature cells that are undergoing continual cell cycling.  Cells are accumulating not due to the speeding up of the cell cycle itself, but by the fact that in comparison to healthy tissue, more cells are going through cell cycling and at times fewer cells are quiescent (inactive/dormant) or going through apoptosis.  The morphology of these cells typically reveals that they are immature and undifferentiated.   This may make sense as it is known that cells that go through cycle cycling are typically immature and haven’t exited the cell cycle to differentiate and mature.   Under the microscope these cells are likely graded as dysplastic (pre-cancerous, slightly immature) or anaplastic (fully immature and cancerous) based on their appearance (e.g. altered cell membranes and organelles) and growth patterns (over-lapping, clustered, homogeneity of cell type etc.).  Most cancerous cells exhibit aneuploidy (too few or too many copies of some chromosomes) which is suspected to play a role in their rogue style of survival.

Cancerous cells typically have altered surface antigens and lost their cell contact inhibition abilities.  Cell contact inhibition, is the ability of most human cells to sense the presence and pressure of neighbouring cells and take that as a clue to stop growing.  Cancerous cells have lost this ability and continue to go throught mitosis and accumulate.  Additionally, cancerous cells no longer adhere to each other, meaning that they more easily can break loose from the mass and invade other tissues and spread to distant site via the blood or lymphatic vessels.  Interestingly, most cells die during transit, though without treatment, some do establish secondary tumors.  This invasion of tissues and spreading is termed metastasis and often causes systemic effects.  Cancerous cells, if not treated, spread into local tissues and metastasize distantly forming secondary sites of cancerous growth.  Common secondary sites include: lungs, liver, bone and brain.  Unlike benign tumors, malignant tumors can recur if removed and are also more likely to be life-threatening if not removed, as they cause tissue destruction which leads to organs failing.

There is a naming pattern for malignant tumors, in that the suffix -carcinoma is frequently used (e.g. adencarcinoma = malignant tumor comprised of epithelial glandular cells).

The Greek physician Hippocrates (460-370 B.C.) is credited with being the first to use the terms carcinos and carcinoma which translate to crab.  This was based on the appearance of cancerous malignant tumors spreading with finger-like projections making them look like crabs.  If you are a familiar with astrology, you may know the sign for Cancer is in the shape of a crab, though the associated constellation of stars looks more like a lobster or crayfish.

Types of Malignant Tumors and Naming Patterns

Cancers can technically arise in any cells that can divide and are often named based on the cell type of origin.  It is worth remembering that there are 4 tissue types of the human body:  epithelial tissue, connective tissue, nervous tissue and muscle tissue.  This is reflected in the naming patterns of cancers.

1. Carcinomas:  The most common type of cancers are comprised of epithelial cells, and account for 90% of all cancers.  It is thought that lymphatiThe suffix -carcinoma is frequently used to name these types of cancers.  For example:
   • Adenocarcinomas: epithelial cancers in a gland
   • Squamous cell carcinoma: epithelial cancers originating in the skin
     • However there are exceptions to this naming pattern, for example:
   • Melanomas: epithelial cancers originating in the melanocytes of the skin
2. Sarcomas: Cancers can also arise in connective tissue and muscle tissue (i.e. mesenchymal tissue, e.g. bone, muscle, cartilage), are usually very malignant and are given the suffix -sarcoma.  For example:
   • Osteosarcoma: bone cancer
   • Rhabdomyosarcoma: cancer of the striated muscle
   • Chondrosarcoma:  cancer of the cartilage
3. Glioma:  This category consists of cancers of any one (or combination) of the four types of neuroglial cells, though more commonly these three neuroglial cell types are involved:
   • • astrocytoma = cancer of the astrocytes (scaffolding and support neuroglial cells)
     • ependyoma = cancer of the ependymal cells (cells that line the brain ventricles and central canal that produce cerebrospinal fluid, CSF)
     • oligodendroglioma = cancer of the oligodendrocytes (myelin sheath cells)
4. Unique Nomenclature:  Several malignant tumors have unique names: Hodgkin’s disease, Wilms’ tumor, Leukemia, Lymphoma, Ewing Sarcoma

Immune Response to Cancer and Metastasis – Almost Perfect?

It is apparent that for cancerous cells to establish themselves, they have to evade the immune system.  In previous sections, it was noted that several leukocytes (i.e. White Blood Cells, WBCs) are capable of destroying cancerous cells.  Natural killer cells insert perforin portals causing cancerous cells to lyse.  Cytotoxic T lymphocytes (i.e. CD8 cells) are capable of causing lysis of cancerous cells using perforin, lymphotoxin or even by inducing the cell to undergo apoptosis.  It is thought that most cancerous cells that do occur are successfully destroyed by the immune system.  It has been found that when the immune system is compromised, for example when a person is immunocompromised due to an underlying disease (e.g. AIDS), they are more likely to develop cancers.

Think About Questions:

What is fibroma?  benign fibrous tissue tumor

Does brain cancer more commonly refer to cancer of the neuroglial cells or neurons?

What is oncology?  Study of malignant tumors (cancer)

What is carcinogenesis?

What is oncogenesis?

Name that cancer?

• Lung carcinoma: most often lung cancer begins in epithelial cells (e.g. glandular or squamous epithelial cells)
• Breast carcinoma: most often start in glandular epithelial cells (so can be called adenocarcinomas)
• Cervical carcinoma: most often cervical cancer begins in epithelial cells (e.g. glandular or squamous epithelial cells)
• Prostate Cancer: remembering that the prostate is a gland, this type of cancer is an adenocarcinoma
• Liposarcoma: cancer of adipose tissue