USMLE PRACTICE QUESTION #103
TOPIC: Reproductive Oncology/Pharmacology
Question #103 will test your understanding of a highly-tested USMLE Step 1 reproductive oncology/pharmacology concept.
I’m Paul Ciurysek, MD, founder of The USMLE Guys, and this is The USMLE Times. This daily newsletter aims to provide super high-yield USMLE concepts commonly tested on exam day. All content is FREE! If you’d like to work with me and my team, please see the options at the bottom of today’s newsletter. Please share the newsletter with a friend if you’d like to support our efforts!
A 48-year-old woman presents to her oncologist for a follow-up appointment after being diagnosed with estrogen receptor-positive breast cancer. The oncologist prescribes tamoxifen as part of her treatment plan. Which of the following best describes the mechanism of action of tamoxifen in the treatment of estrogen receptor-positive breast cancer?
A) Competitive inhibition of estrogen at the estrogen receptor
B) Inhibition of estrogen synthesis by blocking aromatase enzyme activity
C) Noncompetitive inhibition of estrogen at the estrogen receptor
D) Direct inhibition of tumor growth by inducing apoptosis in cancer cells
E) Selective activation of estrogen receptors in the bone, liver, and uterus
F) Reversible inhibition of the progesterone receptor
Detailed Breakdown of Answers + Correct Answer Below ⏬
ANSWER + QUESTION BREAKDOWN
The MENTAL MODEL used to answer this question comes from our detailed test-taking skills masterclass (check it out if you want to elevate your skills). Here’s how to think through this question:
Step 1. Read the last line to get to the heart of the question: “Which of the following best describes the mechanism of action of tamoxifen in the treatment of estrogen receptor-positive breast cancer?”
Step 2: Is this a first-, second-, or third-order question?
Answer: 1st order. 1st: Identify the MOA of tamoxifen.
Step 3: Read the vignette carefully and ask yourself: “What’s the mechanism by which tamoxifen works in estrogen receptor-positive breast cancer?”
Step 4. Look at the answer choices and select the option most closely resembling your final thought from “Step 3” above.
GENERAL ANALYSIS
This vignette describes a 48-year-old woman with estrogen receptor-positive (ER+) breast cancer who has been prescribed tamoxifen as part of her treatment plan. The question asks for the mechanism of action of tamoxifen in the treatment of ER+ breast cancer.
ANSWER CHOICES:
CHOICE A: Competitive inhibition of estrogen at the estrogen receptor
Explanation: Tamoxifen works by competitively inhibiting estrogen from binding to its receptor in breast tissue. By blocking estrogen's access to its receptor, tamoxifen prevents estrogen from stimulating the growth of ER+ breast cancer cells.
CHOICE B: Inhibition of estrogen synthesis by blocking aromatase enzyme activity
Explanation: Aromatase inhibitors (e.g., anastrozole) block the conversion of androgens into estrogens by inhibiting the aromatase enzyme, thereby reducing overall estrogen levels. Tamoxifen does not inhibit aromatase or reduce estrogen synthesis.
CHOICE C: Noncompetitive inhibition of estrogen at the estrogen receptor
Explanation: Noncompetitive inhibition refers to a type of inhibition where the inhibitor binds to a site other than the active site (allosteric site), altering enzyme function without directly competing with the substrate. Tamoxifen acts through competitive inhibition, directly competing with estrogen for binding to its receptor, rather than noncompetitive inhibition
CHOICE D: Direct inhibition of tumor growth by inducing apoptosis in cancer cells
Explanation: While tamoxifen can lead to apoptosis in breast cancer cells, this effect is secondary to its primary action of blocking estrogen receptors. Although tamoxifen may induce apoptosis in ER+ breast cancer cells, this is not its primary mechanism.
CHOICE E: Failed fusion of the palatine shelves with the primary palate
Explanation: Tamoxifen does have agonistic effects on estrogen receptors in tissues like bone and uterus, which can help prevent osteoporosis but also increase the risk of uterine cancer. While tamoxifen does have selective agonistic effects in certain tissues (e.g., bone and uterus), this option does not explain its primary mechanism in treating breast cancer. In breast tissue, tamoxifen acts as an antagonist
CHOICE F: Failed fusion of the palatine shelves with the nasal septum
Explanation: Progesterone receptors are different from estrogen receptors and are not directly targeted by tamoxifen. Tamoxifen specifically targets estrogen receptors, not progesterone receptors.
FINAL VERDICT…
Tamoxifen is a selective estrogen receptor modulator (SERM) that acts primarily by competitively inhibiting estrogen from binding to its receptor in breast tissue.
In patients with ER+ breast cancer, this prevents estrogen from promoting tumor growth by blocking its signaling pathway. This competitive antagonism at the estrogen receptor is crucial for slowing down or stopping the proliferation of ER+ breast cancer cells.
In other tissues like bone and uterus, tamoxifen may act as an agonist on estrogen receptors, but its primary therapeutic effect in breast cancer treatment comes from its antagonistic action on breast tissue
CORRECT ANSWER: A) Competitive inhibition of estrogen at the estrogen receptor
1) 1-ON-1 STEP 1 COACHING: If you’re looking for a personalized approach and guidance designed for your specific needs, goals, and challenges, then 1-on-1 coaching might be what you’re looking for. Choose between daily sessions with Dr. Paul for four, six, or eight weeks. CLICK HERE TO LEARN MORE ABOUT 1-ON-1 COACHING.
2) 1-ON-1 STRATEGY SESSION: If you need some guidance or a plan to get to where you’re going, join me for a 1-on-1 strategy session. This will help you clarify a plan, identify and overcome potential challenges, and give you the best chance for a smooth ride from where you are now to where you’re going. These are done 1-on-1 with me (Dr. Paul), so space is limited. SET UP YOUR 1-ON-1 STRATEGY SESSION HERE
3) THE MASTER CLASSES: I've created two masterclasses based around two of the most commonly experienced challenges I've helped students overcome in the last 15+ years: Test-taking skills and How to get into Residency. These will give you the knowledge, skills, and tools to crush your USMLE exams and match into your dream Residency program. LEARN ABOUT THE MASTERCLASSES HERE
4) ASSESSMENT EXAMS: Save those valuable NBME assessments! Our assessment exam platform was designed to help you identify your strengths, weaknesses, and exam readiness without prematurely wasting your NBME exams. With our USMLEDx assessment platform, you can assess yourself early and often while saving those highly valuable NBMEs for the final stretch of your exam prep. CHECK OUT THE ASSESSMENT EXAM OPTIONS HERE
That’s it for question 103!
See ya tomorrow 👋