## Core Concept
Trastuzumab is a monoclonal antibody that targets the **HER2/neu receptor**, which is overexpressed in certain breast cancers. It works by binding to the HER2 protein, preventing receptor dimerization and subsequent signaling that promotes cell proliferation. This mechanism is crucial in the treatment of HER2-positive breast cancer.

## Why the Correct Answer is Right
Trastuzumab's mechanism involves **inhibiting the proliferation of cells that overexpress HER2**. By binding to the HER2 protein on the surface of cancer cells, trastuzumab blocks the receptor's interaction with other HER receptors, preventing the activation of downstream signaling pathways like the **PI3K/AKT pathway**, which is involved in cell survival and proliferation.

## Why Each Wrong Option is Incorrect
- **Option A:** Without the specific details of option A, we cannot directly address its accuracy. However, if it aligns with known effects or mechanisms of trastuzumab, such as its use in HER2-positive breast cancer or its mechanism of action, it would be considered correct.
- **Option B:** Similarly, without specifics, if option B is a recognized aspect of trastuzumab, such as its administration or side effect profile, and it is accurate, then it wouldn't be the correct answer to the question.
- **Option C:** This option's accuracy depends on its content. If it describes a known benefit, side effect, or characteristic of trastuzumab that is true, then it is not the correct answer to the question.
- **Option D:** Given that the question asks for the statement that is not true regarding trastuzumab and without specific details on the options, **Option D** being the correct answer implies it contains an inaccuracy about trastuzumab.

## Clinical Pearl / High-Yield Fact
A key point to remember about trastuzumab is that it can cause **cardiotoxicity**, leading to heart failure. This side effect is a significant concern and necessitates monitoring of cardiac function in patients receiving trastuzumab, especially when used in conjunction with anthracyclines.

## Correct Answer: D.