What Is Chemotherapy? How It Works, Types and Cycles

How chemotherapy works

Chemo works on cells while they grow and divide. Cancer cells often divide quickly, so chemo affects them strongly. It also affects healthy cells that grow fast, such as those in the hair, the mouth and the gut. That is why hair loss, mouth sores and nausea are common side effects. Most healthy cells recover, and side effects often get better or go away once treatment ends.

Chemo can be used to cure a cancer, to lower the chance that it comes back, or to stop or slow its growth. It can also shrink tumours that cause pain or other problems. It is often combined with surgery or radiation. Given before surgery or radiation, it can make a tumour smaller. Given after, it can destroy cancer cells that may remain.

Chemo is different from targeted therapy and immunotherapy, although they are sometimes given together. Chemo acts on cells that are growing and dividing, including some healthy ones. Targeted therapy finds and attacks specific proteins or receptors that some cancer cells have, while sparing most normal cells. Immunotherapy helps the body's own immune system recognise and attack cancer cells.

Ways chemo is given: IV, oral, injections and others

Chemo can be given in several ways. The method depends on the drug and the type of cancer, and the doctor will explain which way suits the patient.

Chemo can be given during a hospital stay, in an outpatient clinic or doctor's office, or at home. IV sessions are usually done in a hospital or clinic. Oral chemo is usually taken at home.

• IV (intravenous): the most common way. The medicine goes into a vein, usually through a needle in the hand or lower arm. Some patients have a thin tube (catheter) placed in a large vein in the chest, or a small disc placed under the skin (port), that stays in until treatment ends. Sometimes a pump controls how much medicine goes in and how fast.
• Oral: pills, capsules or liquids that the patient swallows.
• Injection: a shot into a muscle or under the skin.
• Other routes, used for certain cancers: into the space around the brain and spinal cord (intrathecal), into the abdomen (intraperitoneal), into the artery that feeds the cancer (intra-arterial), or as a cream on the skin (topical).

How a chemo cycle works

A cycle is a period of treatment followed by a rest period. The rest lets the body recover and build new healthy cells before the next round. For example, a patient might get treatment every day for one week and then rest for three weeks; together that makes one four-week cycle. Depending on the drugs, cycles may repeat every week or every two, three or four weeks or more. A series of cycles is called a course. A course often lasts three to six months and usually has four to eight cycles, but it can be shorter or longer.

Before each cycle, the care team checks how the patient is, does blood tests and asks how the patient is coping with side effects. Based on these checks, the team may delay the next treatment or lower the dose. When possible, it is best to get the full dose and keep cycles on schedule, so do not skip or delay a session on your own. Talk to the team first.

Side effects do not show whether chemo is working, and having few side effects does not mean it is not working. Doctors check the response with physical exams, blood tests and scans such as CT, MRI or PET.

Oral chemo vs IV chemo

Oral chemo is just as strong as chemo given by IV or injection and can cause the same side effects. The difference is where and how it is taken. With oral chemo, the patient takes the medicine at home, so there are fewer treatment visits. It is often taken in on-and-off cycles, and some types are taken every day without a break. The cancer care team still sees the patient and checks progress with blood tests and scans.

Because it is taken at home, more of the responsibility falls on the patient and family. Take the exact dose at the exact time for exactly as long as prescribed. Never change the dose unless the doctor says so. Tell the team about missed or late doses, because this can affect their decisions. Report side effects right away, and check with the team before stopping or changing a dose.

Many oral chemo medicines are considered hazardous. Ask the care team or pharmacist how to handle, store and dispose of the specific drug.

• Other people may need to avoid contact with the medicine and with the patient's body fluids, during treatment and for a time afterward, as the team advises.
• Some pills or capsules should only be handled with gloves.
• Some medicines must stay in their original bottle or box.
• Ask whether the tablets or capsules can be opened, broken, crushed or mixed with food or drink.
• Ask which foods, other medicines, vitamins, herbs and supplements to avoid.
• Some drugs and their packaging need special disposal or must be returned to the pharmacy.

Who decides the chemo plan

The oncologist and the cancer care team decide which drugs to use, the dose and the schedule. They look at the type and subtype of cancer, its stage, results of tests on the tumour (biomarkers), the patient's age, other serious health problems and any past cancer treatment.

Doses are worked out for each person, sometimes from body weight and sometimes from body surface area, which is calculated from height and weight. Doses may be adjusted for people over 65, people with poor nutrition, low blood counts or liver or kidney disease, and people taking other medicines. Two or more drugs are often given together, because drugs that work in different ways can kill more cancer cells and may lower the chance that the cancer becomes resistant. The number of cycles may be set before treatment starts, but sometimes it depends on how the cancer responds.

Patients and families still have a voice. Ask questions, tell the doctor about every medicine and supplement the patient takes, and ask for help getting a second opinion if you want one.

Questions to ask the oncologist

Write your questions down before each visit and note the answers. Bringing a family member to take notes can help.

• Which treatment do you recommend, and why is it best for this patient? What is the goal of treatment?
• How will the chemo be given, and where? How long is each session, and how many sessions or cycles will there be? Will the patient need to stay in the hospital?
• How will we know whether the treatment is working?
• What side effects can happen during or between sessions? Which ones should we call you about right away? Are there lasting effects, including effects on fertility?
• How can side effects be prevented or treated?
• Should we tell you about vitamins, herbs or other supplements? Could any medicines or supplements change how the treatment works?
• Should a family member come to sessions? Can the patient keep working?
• For oral chemo: what do we do if a dose is missed, a pill is lost, or the patient vomits or cannot swallow? How do we store and throw away the medicine?
• How do we reach the team at night or on weekends?
• Would a clinical trial be right for this patient? Can you help us get a second opinion?
• What will treatment cost, and who at the hospital can help us apply for financial assistance?

Paying for chemo and getting the medicines

Many families in the Philippines get help with treatment costs through PhilHealth, the DOH Cancer Assistance Fund at designated hospitals, guarantee letters (GL) from PCSO and DSWD, and help from the Office of the President. The Office of the Vice President says its Medical and Burial Assistance Program has no approved budget under the 2026 national budget, so check with the OVP before applying there. Coverage, requirements and processes change often, so confirm the current rules with the agency itself or with your hospital's medical social service office before you apply.

If your oncologist prescribes chemo for you to buy, 2MG Inc., a Philippine FDA-licensed importer, distributor and wholesaler of oncology and hematology medicines, can help. You can upload the prescription online, and a pharmacist checks every one. Medicines that must stay cold are sent in cold-chain packaging. 2MG is an accredited provider for PCSO, DSWD, OVP and OP guarantee letters and issues official price quotations for assistance applications; PCSO asks for three quotations from different suppliers, and ours counts as one. Senior Citizens and PWDs get a 20% discount and VAT exemption on medicines (on a 2MG order, use either this discount or a guarantee letter, not both). For prices, see our price list.