Chemotherapy for breast cancer I

Proceeding my mother’s recent diagnosis of of HER2 positive invasive ductal carcinoma, I thought I’d initiate a series of blog posts both tracking my own mother’s treatments and researching the field of oncology. I want to ensure that these articles are conveyed sensitively thus I shan’t provide any explicit details concerning my own mother, but the situation I am now in has allowed me to witness and experience first hand the trauma of cancer. The realisation of what a patient must overcome, both mentally and physically, was shocking to me.

Firstly,  prior to explaining any forms of treatment, I needed to establish just what is meant by HER2 positive. IHC, or ImmunoHistoChemistry, is a special staining process performed on fresh or frozen breast cancer tissue removed during biopsy. IHC is used to show whether or not the cancer cells have HER2 receptors and/or hormone receptors on their surface. IHC is the most commonly used test to see if a tumour has too much of the HER2 receptor protein on the surface of the cancer cells. With too many HER2 receptors, the cells receive too many signals telling it to grow and divide. The IHC test gives a score of 0 to 3+ that measures the amount of HER2 receptor protein on the surface of cells in a breast cancer tissue sample. If the score is 0 to 1+, it’s called “HER2 negative.” If the score is 2+, it’s called “borderline.” A score of 3+ is called “HER2 positive.”

HER2-positive breast cancer is a breast cancer that tests positive for a protein called human epidermal growth factor receptor 2 (HER2), which promotes the growth of cancer cells. In about 1 of every 5 breast cancers, the cancer cells make an excess of HER2 due to a genetic mutation on chromosome number 17. This gene mutation and the elevated levels of HER2 that it causes can occur in many types of cancer — not only breast cancer. This is a gene mutation that occurs only in the cancer cells so causes a marked increase in the number of HER2 receptor molecules at the membrane of tumour cells. This perpetuates the rapid growth of the tumour, therefore HER2-positive breast cancers tend to be more aggressive than other types of breast cancer. They’re also less responsive to hormone treatment.

Due to the fact steroid treatments are ineffective in combating the HER2+ tumours, the drug trastuzumab (Herceptin). Herceptin works by attaching itself to the HER2 receptors on the surface of breast cancer cells and blocking them from receiving growth signals. By blocking the signals, Herceptin can slow or stop the growth of the breast cancer. Herceptin is an example of an immune targeted therapy. In addition to blocking HER2 receptors, Herceptin can also help fight breast cancer by alerting the immune system to destroy cancer cells onto which it is attached.

Herceptin causes flu-like symptons in about 40% of the people who take it. These symptoms may include:

  • fever
  • chills
  • muscle aches
  • nausea

However, less commonly, Herceptin can cause damage to the heart and affect its ability to pump blood effectively. This risk has ranged between 5% to 30%. The damage can be mild and result in either no symptoms or signs of mild heart failure, like shortness of breath. Less commonly, the heart damage is bad enough that people experience life-threatening congestive heart failure or a stroke. The risk of heart damage, especially severe damage, is greater when Herceptin is given along with other chemotherapy medicines known to cause heart damage. Adriamycin is an example of a chemotherapy that can cause heart damage.

Herceptin can rarely cause two possibly related serious reactions that interfere with breathing. One of these is a reaction during or shortly after Herceptin is being administered. This is like a bad allergic reaction, with symptoms that  include wheezing and trouble breathing due to sudden swelling and narrowing of the airways. The other reaction, called pulmonary toxicity, results in swelling of the lung tissue, low blood pressure, and possibly pleural fluid build up around the lungs (called pleural effusions).

Following my mother’s first round of chemotherapy, she was provided with a pre-filled syringe containing 6mg of Pegfilgrastim. This is a drug that is commonly used to reduce the chance of infection in people who have certain types of cancer and are receiving chemotherapy medications that may decrease the number of neutrophils. Pegfilgrastim is in a class of medications called colony stimulating factors. It works by helping the body make more neutrophils. Owing to the fact I want to become a doctor, my mother allowed me to make the subcutaneous injection.

 

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