Cancer is different from viral/bacterial infection.Cancer does not involve antigenes or foreign structures in the body. Yeah, there is an exception in the form of onkoviruses, but most of the cancers are connected with abnormal growth of tissue (abnormal division of cells) due to defect in their DNA. Body has lost the ability to control the growth of cells (and even to control their apoptosis), but still they are body cell, not antigenes and that’s why (i think it works this way:) ) immune system does not recognise them.

but researchers r continuein to find ways to treat this cancer…read this article abt one of the researches
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Cancer cells secrete chemokin that prevents immune cells to recognize them.

A cancer is always genetic, that is, it’s always a result of DNA alterations. Generally, a cancer is a result of alterations in the mechanisms that control cell divisions.
While with the technology development there are much more subtances capable of making damage to DNA, the truth is that biotechnology made it possible to act in that molecule. Every agent responsible for a mutation is called a mutagenic agent. The process of mutation is called mutagenesis.
Those are high energy radiations, x ray, gamma ray, particules emmited by radioactive substances but also chemical substances like colourants and preservatives and components of a cigarett. Cells can repair damage caused to DNA, exg the role of DNA polymerase and some enzymes.
But sometimes the equilibrium between damage repair and mutagenesis is broken.
Cancer (or malign tumor or malign neoplasia) refers to a group of diseases that have in common the fact that they always present the growth of a neoformed tissue.
In fact, a pluricellular organism is a result of the equilibrium between cell proliferation and apoptosis. There are two main ways for cell death: necrosis and apoptosis.
While the first one is the mechanism by which a cell dies because of toxic substances or lack of essential nutrients with a small infection, apoptoses is a set of phenomenons genetically programmed for cell death.
When cells present abnormalities or are not needed anymore to the organism, they start to isolate from other cells, there’s a compactation of chromatin and cytoplasm, DNA is fragmented in small fragments through the enzyme endonuclease, without rupture and thus no inflammatory response.
In a normal organism cell division is contra-balanced with apoptosis. When this equilibrium is broken cancer may occur.
So, as a neoplasia is a result of genetic modifications, those modifications may change the mechanism that allows cell division and apoptosis. When the mechanism of cell proliferation is altered, it’s a result whether from a more stimulation for cell division or an alteration what will inhibit cell division. In the first case it’s an alteration in proto-oncogenes and in the second one is in tumor suppressor genes.
Proto-oncogenes are capable of stimulating cell divisions. They are usually inactivated in cells that do not divide. Because of mutagenic agents, whether biologic, chemical or physic, these genes may stimulate cell division permanently, turning onto oncogenes.
Tumor suppressor genes contra-balance the proliferation power of proto-oncogenes. They have an inhibit action. They are usually activated thus blocking cell division. Mutagenic Agents may alter modify them and cells remain dividing themselves.
The organism is capable of naturally deleting neoplasic cells. However when that does not happen, cancers starts (when cells genetically altered proliferate). In some cases cancer cells may migrate to other sites of the organism and develop there, a process called metastasis.
Cancer may also be hereditary but is rare. When that happens, all cells have altered DNA and cancer starts earlier. Almost all of them are sporadic cancers that result of somatic mutations.