Rx Pharm Flashcards
A 40-year-old woman presents to her gynecologist with a lump in her left breast. She is not sure how long the lump has been there, but she first noticed it in the shower 2 weeks ago. She has never had a mammogram and notes that her mother died of breast cancer. On physical exam, the lump is located in the upper outer quadrant of the left breast, and it is very firm and immobile. Additionally, the patient has a few firm lymph nodes in her left axilla. A mammogram is obtained and shows calcifications in the area of the lump. A biopsy specimen is taken and it stains positively for an antibody against the protein produced by mutations in erbB2 (formerly referred to as HER-2/neu). She begins chemotherapy with a drug that is specific to this particular type of breast cancer.
What is the mechanism of action of the drug she was most likely given?
Antibody-dependent cytotoxicity
Trastuzumab is a recombinant human monoclonal antibody to ERBB2 and is used to treat breast cancer. It can cause cardiotoxicity.
OTHERS
Bevacizumab, tamoxifen, paclitaxel, and leuprolide do not have significant roles in treating ERBB2-positive breast cancer.
- Bevacizumab is a monoclonal antibody which decreases angiogenesis by inhibiting vascular endothelial growth factor (VEGF).
- Tamoxifen is a selective estrogen receptor modulator (SERM) that is used to treat breast cancers that highly express the estrogen receptors.
- Leuprolide, when given in a continuous fashion, decreases the secretion of LH and FSH and is used to treat prostate cancer, uterine fibroids, and precocious puberty.
- Although paclitaxel, a disrupter of polymerization/depolymerization of microtubules, is included in breast cancer chemotherapy regimens, its mechanism of action does not include activity against human epidermal growth factor receptor 2.
A 56-year-old man presents with a 6-month history of urinary urgency, urinary hesitancy, lower back pain and a 9-kg (20-lb) unintentional weight loss. His prostate-specific antigen level is 19 ng/mL (normal < 4 ng/mL). MRI of the lumbar spine shows osteoblastic lesions. The physician prescribes a medication, and explains that it requires careful monitoring, since the drug first increases hormone production before therapeutically decreasing it.
Which of the following is the most likely mechanism of action of the prescribed medication?
Inhibition of follicle-stimulating hormone and luteinizing hormone release
Leuprolide, a treatment for metastatic prostate cancer, continuously stimulates GnRH receptors until they are desensitized, causing an initial increase in FSH and LH before inhibiting hormone production. Leuprolide suppresses testicular steroidogenesis and can reduce androgen-sensitive prostate tumors.
OTHERS
- Medications that modulate cortisol and estrogen are not appropriate therapies for metastatic prostate cancer.
- Growth hormone release is not affected by prostate cancer medications.
- Inhibition of testosterone conversion to DHT is used to treat benign prostatic hyperplasia, but does not address high testosterone levels that induce proliferation of prostatic masses.
A 6-year-old girl is brought to her pediatrician because she has seemed pale and fatigued during the past 3 weeks. Physical exam reveals splenomegaly and scattered bruising. Laboratory studies show anemia, thrombocytopenia, and increased blasts on peripheral blood smear. The patient undergoes a bone marrow biopsy and then begins treatment with four medications, one of which is an M-phase-specific agent.
Which of the following drugs has most likely been prescribed for this patient to act on cells during the M-phase of the cell cycle?
Vincristine
Treatment of ALL (acute lymphoblastic leukemia) typically involves several stages. Induction therapy consists of a four-drug regimen that includes an M-phase-specific agent such as vincristine.
OTHERS
None of the other medications act in the M phase.
- Doxorubicin is another chemotherapeutic agent commonly used in the initial stage of ALL treatment. It inhibits DNA synthesis through the generation of free radicals that cause strand breaks. It also has the ability to intercalate (insert) between DNA base pairs, and therefore acts during multiple phases of the cell cycle but not during M phase.
- Methotrexate has a variety of indications and blocks DNA synthesis during S phase.
- Later in S phase and early in G2 phase, etoposide inhibits topoisomerase II.
- Cisplatin is not cell-cycle specific and is more commonly used to treat adult cancers.
A 30-year-old man is referred to a urologic oncologist because of a painless, solid testicular mass. A diagnostic evaluation including scrotal ultrasound, radiographic studies, serum markers, and positron emission tomography scan is performed. The patient is diagnosed with a low-risk disseminated seminoma. The physician tells the patient that standard treatment is three cycles of a combination regimen with etoposide, cisplatin, and a third agent that can cause a serious adverse effect. After 3 months of this treatment regimen, the patient reports new-onset shortness of breath, an unremitting non-productive cough, and increased fatigue.
Which of the following is the mechanism of action of this third agent?
It generates free radicals that cause single double-stranded DNA breaks
Bleomycin acts by producing free radical species that cause single double-stranded DNA breaks. It is often used for treatment of testicular cancer and causes little myelosuppression, but patients need to be monitored for pulmonary fibrosis.
OTHERS
- Although busulfan, an alkylating agent, also can cause pulmonary fibrosis, it is more commonly used for treatment of chronic myelogenous leukemia.
- 6-Mercaptopurine, cytarabine, and 5-fluorouracil are also not used to treat testicular cancer.
- Etoposide can be a treatment for testicular cancer, but it does not result in lung toxicity or pulmonary fibrosis.
A 45-year-old woman comes to her primary care physician because of a new breast lump. She noticed the lump a few weeks ago and she feels that it has grown in size since then. On physical examination, the lump is palpated in the upper outer quadrant of her right breast, and it is non-tender, firm, and immobile. The patient undergoes imaging studies and is diagnosed with stage II breast cancer. Results of a biopsy reveal that the cancer is estrogen-receptor positive. After discussing treatment options with her oncologist, the patient undergoes lumpectomy and chemotherapy. Afterward, her physician starts her on maintenance medications, including one that will increase her risk of endometrial cancer.
In addition to improving her breast cancer prognosis, which of the following is an effect of this medication?
Inhibition of osteoclasts
Tamoxifen is an antagonist to estrogen receptors on breast tissue as well as an agonist to estrogen receptors on endometrial tissues and bone. By increasing endometrial growth, it poses a risk for endometrial cancer. Tamoxifen is associated with an increased risk of endometrial hyperplasia/carcinoma because of its stimulatory effects on the uterus.
OTHERS
- Raloxifene is another SERM used in the prevention and treatment of osteoporosis that reduces risk of breast cancer without increasing the risk of endometrial disease.
- Cirrhosis and ascites are features of liver failure, and are not related to tamoxifen.
- Hyperstimulation of the ovaries can be seen with clomiphene, not tamoxifen.
- Myelosuppression, pulmonary fibrosis, and renal failure are serious complications associated more commonly with other chemotherapeutic agents.
