Cancer is cured when every malignant neoplastic cell is removed from the patient’s body. Neoplastic cells are those with the capacity for uncontrolled replication. Malignant neoplastic cells are (for the most part), those with the capacity to metastasize to other parts of the body (“benign” neoplasms are those that continue to grow ...
Almost 70% of patients with cancer are cured today, meaning that they don’t recur within five years.
Immune modulating drugs may stimulate the immune system to attack the abnormal cells. Killed by blocking key enzymes necessary for cellular proliferation. And others.
Not only do cancer cells continually change how they behave and adapt, these changes can be different in different parts of a tumor. Due to these changes, one part of a tumor may be sensitive to a treatment while another part of the tumor (or a metastasis) may be resistant.
Resistance. Changes in cancer cells lie behind much of the resistance to treatment that's seen with cancer. While a tumor may initially respond to a treatment such as chemotherapy or a targeted therapy, cancers often find ways to bypass these treatments and continue to grow.
These nearby cells such as fibroblasts, macrophages, and much more can be coerced to secrete compounds that help a tumor grow. (This recruitment of normal cells to do the dirty deeds of a cancer is something that can't be studied in a dish in the lab, and adds to the challenges of understanding and treating cancer).
Two cancers of the same tissue type, subtype, and stage may have significant molecular differences; differences that can play a considerable role in available treatment options and outcome. This isn't surprising as cancer therapy can be seen as analogous to the treatment of infectious disease.
Cancers That Are Currently Curable. Stage 0 cancers, such as ductal carcinoma in situ (DCIS) should in theory be 100 percent curable as they are not considered invasive (they haven't spread beyond something called the basement membrane).
Most drugs for cancer are first studied on cancer cells grown in a dish in the lab and in animal studies. Unfortunately, what works in a dish in the lab (in vitro) does not often translate to effectiveness in the human body (in vivo).
The fact that cancer isn't one disease is evident in the conventional treatment approaches. Treatments for lung cancer differ for those of breast cancer, and so on. Yet recent advances are exploiting the similarities between different cancers in order to treat them.