Cancer: Types, Causes, Symptoms and Treatment

Introduction

Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. This (the spread) is called metastasis.
The word cancer was derived from the ancient Greek Kapkívoç, meaning crab and tumor. This was because Greek physicians Hippocrates and Galen, among others, noted the similarity of crabs to some tumors with swollen veins.
Metastasis is the spread of cancer to other locations in the body. The dispersed tumors are called metastatic tumors, while the original tumor is called the primary tumor.
Metastasis is common in the late stages of cancer and it can occur via the blood or the lymphatics system or both.
The steps in metastasis of cancer include;

Local invasion
Intravasation into the blood or lymph
circulation through the body,
extravasation into the new tissue,
proliferation and angiogenesis.

The most common places for metastases to occur are the lungs, liver, brain and the bones. Metastasis to the eye also occur.
Ocular cancers include;

Melanomas-iris, ciliary body and choroidal melanomas etc
Squamous cell carcinoma
Retinoblastoma
Lymphoma

Classification of Cancer

Cancers are classified by the type of cell that the tumor cells resemble and
is therefore presumed to be their origin.
These types Include:

1. Carcinoma

Carcinoma are cancers derived from epithelial cells. This group includes many of the most common cancers which are the breast, prostate, lung, pancreas and colon cancers.

2. Sarcoma

Sarcoma are cancers arising from connective tissue (i.e. bone, cartilage, fat, nerve), each of which develops from cells originating in mesenchymal cells outside the bone marrow.

3. Lymphoma and leukemia

These two classes arise from hematopoietic (blood-forming) cells that leave the marrow and tend to mature in the lymph nodes and blood, respectively.

4. Germ cell tumor

Cancers derived from pluripotent cells, most often presenting in the testicle or the ovary (seminoma and dysgerminoma, respectively).

5. Blastoma

Cancers derived from immature “precursor” cells or embryonic tissue.

Causes of Cancer

Genetic mutations due to environmental and lifestyle factors. This occurs in 90 95% of cases. These factors include tobacco, diet and obesity, infections, radiations, lack of physical activity and pollution.
Inherited genetics. This occurs in 5-10% of cases

Others causes include:

Physical agents such as asbestos, glass wool and metallic cobalt
Hormones e.g, Insulin-like growth factors.
Autoimmune diseases e.gs with Crohn’s disease and ulcerative colitis

Pathophysiology

Cancer is a disease of tissue growth regulation. In order for a normal cell to transform into a cancer cell, the genes that regulate cell growth and differentiation must be altered. The affected genes are divided into two broad categories. These are the

The oncogenes: these are genes that promote cell growth and reproduction
The tumor suppressor genes: these are genes that inhibit cell division and survival.

Malignant transformation can occur through the formation of oncogenes, the inappropriate over-expression of normal oncogenes or by the under expression or disabling of tumor suppressor genes. Typically, changes in multiple genes are required to transform a normal cell into a cancer cell
Genetic changes can occur at different levels of chromosome. The gain or loss of an entire chromosome can occur through errors in mitosis.
Mutations may involve the deletion or gain of a portion of a chromosome.
Genomic amplification occurs when a cell gains copies (often 20 or more) of a small chromosomal locus, usually containing one or more oncogenes and adjacent genetic
material.
Translocation occurs when two separate chromosomal regions become abnormally fused often at a characteristic location.

Epidemiology

Ocular cancers are rare and they constitute less than 1% of all cancers. The average annual incidence rate in USA is about 1 in 100,000 population. The prevalence rate is about 12 in 100,000 population. The incidence of ocular and adnexal cancer are low. While retinoblastoma occur in children, melanomas and squamous cell carcinoma are found mainly in middle age and adult. They mostly occur in equal frequencies in both sexes

Clinical Features of Cancer

Most cancers are initially recognized either because of the appearance of signs or symptoms or through screening. Neither of these leads to a definitive diagnosis, which requires the examination of a tissue sample by a pathologist.

Systemic features

These usually manifest in advance cases and depend on the type of cancer

Fever
Cough
Headache
Weight loss
Night sweat
Irritability
Malaise

Ocular features

Ocular features also depend on the type of cancer. Generally, there could be

poor vision
protrusion of the eye
Hyphema
uveitis
Vitritis
Vitreous hemorrhage
Retinal hemorrhage
Retinal detachment

Examination

General examination
Ocular examination:
- Check visual acuity
- Anterior segment for uveitis, hyphema, tumor seeding
- posterior segment for vitritis, retinal detachment, tumor location

Investigation

Investigation of cancer depends on the type. These could include:

full blood count
X-rays,
CT scans
MRI
Endoscopy.
Biopsy

Ocular investigation

Ultrasound is used to assess tumor size.
CT scan to detect tumor location.
MRI is superior to CT scan for optic nerve evaluation and detection of
extraocular involvement.
biopsy.

Treatment

Treatment depends on the type of cancer, location of cancer, metastasis

Systemic cancer

Treatment options include;

pharmacological such as chemotherapy which kills cancer cells
Hormonal therapy; slows or stop the growth of cancer cells e.gs breast and prostate cancers
Immunotherapy; helps immune system to fight infection
Radiation therapy; uses high doses of radiation to kill and shrink cancer cells
Stem cell transplant; it restores blood forming stem cells in cancer patients
Surgical
Targeted therapy; it targets the changes in cancer cells that help them grow.

Ocular cancers

Treatment modalities include;

Chemotherapy to shrink the tumor
Photocoagulation
Cryotherapy
Radiotherapy
Surgery

Ocular Treatment Using Retinoblastoma

1. Small tumors no more than 3mm diameter and 2mm thickness may be treated as follows:

Photocoagulation using a low-energy 532nm argon or 810nm diode laser. At least three treatment sessions are needed.
Cryotherapy is useful for pre-equatorial tumors without either deep invasion or vitreous seeding. Repeated treatment may be necessary.
Chemotherapy without other treatment for a macular tumor to conserve as much vision as possible.

2. Medium sized tumours up to 12mm diameter and 6mm thickness may be treated as follows:

Brachytherapy using iodine-125 or ruthenium-106 is indicated for an anterior tumor if there is no vitreous seeding.
Primary chemotherapy with intravenous carboplatin, etoposide and vincristine (CEV) is given in three to six cycles. Single agent chemoreduction with carboplatin alone has recently been found to give similar results as multi-agent therapy.

3. Large tumor >12 mm in diameter

Chemotherapy to shrink the tumor
(chemoreduction). Chemotherapy also will have a beneficial effect if a smaller tumor is present in the fellow eye or if there is a pinealoblastoma.
Enucleation is indicated if there is vitreous haemorrhage or optic nerve invasion. It is also performed if chemoreduction fails or a normal fellow eye makes aggressive
chemotherapy inappropriate.

References

Cancer A-Z. American Cancer Society website. Accessed October 6, 2021
Cancer Causes and Prevention. National Cancer Institute. Accessed October 6, 2021
Cancer. WHO. Accessed October 6, 2021
Suzanne Dixon, MPH, MS, RDN. What Should I Know About Lung Cancer Caused by Asbestos?. Asbestos.com. Accessed October 6, 2021
Cooper GM. The Cell: A Molecular Approach. 2nd edition. Sunderland (MA): Sinauer Associates; 2000. The Development and Causes of Cancer. Accessed October 6, 2021