Cancer is not one disease. It is a group of more than 100 different diseases that share common symptoms.
A cancer is a disease that causes abnormal cell growth (a tumour), which has the potential to spread to another part of the body (metastasis). Most cancer deaths are caused after the primary tumour has metastasised.
The cells have been genetically altered, through bad divisions or radiation damage, causing problems in the normal life cycle of the cell.
Cells in the body are programmed to die when they receive certain signals. Cancerous cells ignore those signals and continue to grow regardless. Cells are usually limited in the number of time that they can divide (called the Hayflick limit), but cancerous cells continue to divide, producing further cancerous cells.
30-35% of all cancer deaths are caused by bad diet and obesity. 25-30% by tobacco, 15-20% by infections, up to 10% by radiation. 5-10% are genetic in nature, built into the body at birth. Other minor causes are stress, lack of exercise, and environmental pollutants.
In the developing world, about one third of cancers are caused by tobacco, and 20% are caused by infections such as human papillomavirus (HPV), hapatitis B, hepatitis C.
This chart shows the incidence of death from trachea, bronchus and lung cancers over the last 15 years in 30-49 year old Irish adults. It should be noted that Ireland introduced a ban on smoking in workplaces in 2004. I think the chart shows strong evidence that the ban works:
To avoid getting cancer: don’t smoke, keep a healthy weight, don’t drink too much alcohol, eat properly, vaccinate (HPV, for example), reduce meat in your diet, and don’t spend too much time in the sun. The most common cancer is skin cancer (40%). 90% of skin cancers are caused by sunlight exposure. So, by avoiding direct sunlight, you cut the chance of you dying by cancer by more than a third (36%).
In 2015, 15.7% of all deaths were from cancer.
Because cells are so small, it is impossible for us to know when cancer starts. We cannot know until it becomes noticeable. Sometimes, this starts by creating small problems that are then misdiagnosed as other diseases.
Treatments of cancer depend on the location, type of cancer, it’s stage, and how healthy the patient is.
If the tumour is well-defined and not connected directly to the blood circulatory system, then surgery can cure the problem. The surgeon will excise the entire tumour, making sure to remove even the smallest trace. If any cells at all are left behind, then they can metastasise to somewhere completely different in the body that is much more difficult to treat. Common areas for surgery include the breast, lung, prostate.
Radiation therapy can be used if surgery is deemed dangerous. Radiation therapy involves blasting the cancerous area with X-rays, causing breaks in the DNA of the cancerous cells, and any healthy cells that are in that immediate area. Once the DNA is broken, the cells are unable to divide, and die off. Radiation therapy is dangerous in young patients, causing significant effects that affect the child in later life. Radiation is also not recommended in brain cancers, because it can cause a lowering of intelligence.
Chemotherapy involves treating cancers with chemicals. The chemicals indiscriminately attack all rapidly dividing cells, which can mean that healthy tissue (such as intestinal tissue, which has a high replacement rate) can be damaged during the treatment. Healthy cells can usually heal themselves, though, so the idea is to attack and kill as much cancer as possible and then let the body recover from the onslaught. Some chemotherapies involve using total body irradiation as well, which can destroy your bone marrow, so before the treatment, bone marrow is harvested, and replaced after treatment.
Immunotherapy involves training the immune system to recognise and destroy cancer cells. It has a surprisingly long history. 4600 years ago, the Egyptian polymath Imhotep described breast cancer. In one story, he describes a treatment for it - creating an infection in the tumour and allowing the immune system to eat up the cancer while it is taking care of the infection.
In another story, a Christoan priest, Peregrine Laziozi was afflicted in the 14th century with cancer of the tibia which required his leg to be amputated. The lesion grew so much that it broke through the skin of the leg and got infected. His immune system ate the cancer as well as the infected area, and when the surgeon was scheduled to amputate the leg, the cancer had "miraculously" vanished.
The first time the underlying cause of this was recognised was in 1891 when William Coley, a bone surgeon, came across records of a patient who had a huge sarcoma on his cheek. Despite two surgeries, the sarcoma persisted. After the second surgery, the wound was too large to suture closed and skin grafts were unsuccesful. The wound became infected and the patient developed a fever. After each fever attack, though, the ulcer receded, until finally the tumour vanished completely. He was eventually discharged with a large scar on his cheek, but no cancer.
Coley at first thought that the bacteria that was infecting the cheek was the cause of the cancer cure, but later realised that it was the body's reaction to infection that was the real cause.
He used this knowledge to develop a vaccine that could cause an immune response in the body. Some of his test patients died because the infection was too strong. Some didn't respond at all to the vaccine. But in some, the body reacted just as he wanted, and the cancer was cured. His largest success was in treating a man who had cancer in the bladder, pelvis and abdominal wall. After treatment and recovery, the patient lived a further 26 years before dying of a heart attack.
Coley stressed that the fever part of the infection was the key to successful treatment, and this was proven when a retrospective study showed a 60% survival rate in people that had fevers during treatment, vs 20% survivain people that had no fever.
In 1985, Steven Rosenberg found a way to activate immune responses target against specific cancers, using T-cell growth factor to bring about tumour regression. This let to a very successful 2.6-3.3% regression rate.
In 1987, it was discovered that one defence that cancer cells have is that the lymphocyte CTLA-4 prevents T-cells from attacking cancer cells. J P Allison found that by developing antibodies that specifically blocked CTLA-4, he was able to induce the destruction of cancer in mice. It took some time, but in 2010, it was reported that human trials showed this could extend expected life in advanced melanoma from 6 months to 10 months.
In the early nineties, another molecule that disables T-cells was discovered and called PD-1 (programmed death 1). An antibody for this was developed and in 2013, it was found that this antibody shrank tumours by more than half in 31% of melanomes, 29% of kidney cancers, and 17% of lung cancers.
In 2006, Steven Rosenberg, who had been the first to use T-cells to attack cancer, genetically engineered a lymphocyte to treat a metastatic melanoma. His team expanded on this method to produce a system called Chimeric Antigen Receptor therapy that can produce personalised antibodies from a patient's own immune system. This results in complete remission in most (60%) leukemias.
Researchers are finding new tricks to stop cancer all the time. In May 2017, it was announced that the common painkiller aspirin may reduce the chance of metastatis. What happens with metastasis is that the cancer tumour convinces platelet cells to open walls in veins to allow tumour cells through, the tumour cells sneak through into the blood vessels cloaked from the immune system in a shield of platelets, and when the cells have traveled a bit down stream, the platelets are instructed to produce growth hormone, creating new blood vessels to feed the migratory cancer cells. Aspirin interferes with cancer cells' ability to co-opt platelets in this way, leaving the tumour cells naked to the immune system, reducing the chance of metastasis. Taking aspirin daily can cause serious side-effects such as bleeding, so it's not something you should just add to your daily regimin without thinking about it first. Having said that, women that take 3 low dosage aspirins every week are less likely to get breast cancer in the first place.
June 2017, prostate cancer gets a boost, as it is discovered that by combining the drug abiraterone with the standard treatment ADT, the three-year chance of survival increases from 76% to 83%. In other words, were there was a 1/4 chance of dying within three years, that is now 1/6.