If something is growing abnormally, it makes sense to cut it out. Indeed, surgical removal of tumor (i.e., enlarged tissue) was the first successful treatment of cancer surgeons attempted in the 19th century. Surgery remains a conventional method to treat solid cancers today (for example, prostate and breast cancers). However, it cannot be used for liquid cancers (for example, blood- and bone marrow cancers), or when a solid cancer have spread (metastasized) to other tissues.

During surgery, the surgeon removes the visible tumor, as well as some of the surrounding healthy tissue to create a safety margin. Sometimes, nearby lymph nodes will be removed as well and analyzed for metastatic spread of the cancer. In prostate cancer, such surgery is called radical prostatectomy; in breast cancer, it is mastectomy and lumpectomy (i.e., partial mastectomy, where only a portion of the breast is excised).

Within a year of the discovery of X-rays in 1896, physicians started using X-rays to treat breast cancer. However, radiotherapy was not very successful at that time due to insufficient knowledge of how radiation works. As science progresses over the decades, professionals now understand how radiotherapy is best used to treat cancer.

Radiotherapy relies on ionizing radiation, such as X-rays and radioactive materials (e.g., iodine, iridium, lutetium), to kill dividing cells by damaging its DNA. Since cancer cells divide much faster than normal cells, they are more susceptible to radiation killing. Types of radiotherapy commonly used to treat prostate and breast cancer are external-beam radiation and in selected cases brachytherapy. In external-beam radiotherapy, a machine delivers radioactive rays onto the tumor. Brachytherapy involves implanting radioactive materials in the form of small seeds, wires, or catheters inside or near the tumor.

Chemotherapy means using cytotoxic chemical compounds to kill cancer. They can be considered as anti-cancer drugs. Its first success was in 1946, when researchers repurposed mustard gas used in wars to treat lymphoma. Since then, increasingly more chemotherapy drugs have been developed and approved for medical use, and each attacks cancer differently. Some directly break DNA strands, some inhibit DNA or RNA synthesis, some block protein production, some prevent cell division, and some are better apt at entering certain organs.

For prostate cancer, such drugs include docetaxel (Taxotere), Cabacitaxel, and in rare situations also mitoxantrone, doxorubicin, vinblastine, paclitaxel. In breast cancer, common chemotherapeutic drugs include doxorubicin, capecitabine, paclitaxel, docetaxel, and carboplatin. As these drugs have their unique mechanisms of killing cancers, they are usually used in combinations for maximal efficacy. Importantly, it is also more difficult for cancer cells to develop resistance to two drug mechanisms at the same time.

Testosterone, estrogen, and insulin are examples of hormones that signal the cell to do something, such as triggering protein production or cell growth. Some cancer cells respond to these hormonal signals, which they exploit to fuel their growth into an enlarged tumor. Therefore, hormonal therapy aims to starve cancer cells of hormones important for their cell division or growth.

For example, androgen deprivation therapy (ADT) is used to treat prostate cancer. Over 90% of androgens are testosterone, which prostate cancer cells rely on for growth. ADT can be achieved with surgical removal of the testicles (i.e., orchiectomy) or drugs that stop testosterone production or block androgen effects on cancer cells. In breast cancer, hormonal therapy aims to reduce the effects of estrogen or progesterone on breast cancer cells. This may be done through surgery, by removing the ovaries (the place where those hormones are made) or drugs that stop hormone production and finally, drugs that block the effects of hormones directly at the cancer cell membrane level (receptor blocker).

While immunotherapy has its roots in China’s Qin dynasty period, it is only recently used to treat cancer, where drugs are used to enhance the immune system to recognize and destroy cancer cells. Indeed, our immune system has a built-in anti-tumour activity through specific immune cells (e.g., natural killer cells, macrophages, and T-cells), which recognize cancer cells as foreign entities and initiate killing. For this reason, cancers have evolved mechanisms to turn off such immune system activities as they are growing into a tumor. So, certain immunomodulators have been developed to stimulate the anti-tumor immune system.

For example, Sipuleucel-T cancer vaccine has been approved to treat metastatic prostate cancers resistant to hormonal therapy. This immunotherapy stimulates T-cells (i.e., a type of white blood cell) to attack cancer, acting similarly as vaccines that train the immune system against infectious diseases. Pembrolizumab, a so-called check-point inhibitor, is another approved immunomodulator used for advanced prostate and breast cancers with certain mutations. Several antibody-based drugs have also been approved for breast cancers, although each has their suitability designed for specific cancers subtypes.