Understanding clinical studies - p value

The P (probability) value is used when we wish to see how likely it is that a hypothesis is true. The hypothesis is usually that there is no difference between two treatments, known as the “null hypothesis”.

P = 0.5 means that the probability of the difference having happened by chance is 0.5 in 1, or 50:50.
P = 0.05 means that the probability of the difference having happened by chance is 0.05 in 1, i.e. 1 in 20. = SIGNIFICANT result

The lower the P value, the less likely it is that the difference happened by chance and so the higher the significance of the finding.

P = 0.01 is often considered to be “highly
significant”. It means that the difference will only have happened by chance 1 in 100 times. This is unlikely, but still possible.
P = 0.001 means the difference will have happened by chance 1 in 1000 times, even less likely, but still just possible. It is usually considered to be “very highly significant”.

Resources

http://www.roche.com/research_and_development/what_we_are_working_on/oncology/cancer-immunotherapy/interpreting-clinical-trials-data.htm
MedicalStatisticMadEasy

What's in a name?

What is cancer? 

Cancer is an uncontrolled cell proliferation. The term cancer is synonym with malignancy. Benign tumours are not cancer. 
Because dividing cells do not always copy their DNA perfectly, every division is an opportunity for a cancer-causing mutation. The difference in cancer rates in different tissues can  be the result of different underlying rates of cell division. As an argument,  cells of the large intestine divide frequently,  (approximately 4.3 percent of men and women will be diagnosed with colon and rectum cancer at some point during their lifetime)  while small bowel cancer, which has cells that divide rarely,  is rare (approximately 0.3 percent of men and women will be diagnosed with small intestine cancer at some point during their lifetime).

 Results from a recent study show that random DNA copying mistakes are responsible for 66% of the mutations (aka bad luck according to the authors) 29% are due to environmental factors and 5% of heredity. This study is controversial, and more reliable studies show that roughly 42 percent of cancers are preventable by: not smoking, maintaining a healthy weight, and not being exposed to cancer-causing pollutants. I personally dislike this term "bad luck" and I considere that this is a question to be answered, what causes this mutations or what makes them invisible for the immune system?

What's in a name? Ethymology

 The word cancer comes from the latin  word cancer, meaning crab, since the enlarged veins seen in some cancer resembled with the legs of a crab.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3069308/
http://www.sciencemag.org/news/2017/03/debate-reignites-over-contributions-bad-luck-mutations-cancer