Which drug can cause fluid retention requiring careful monitoring during treatment?

Docetaxel is known to potentially cause fluid retention, which can lead to complications such as edema. This side effect is particularly important to monitor during treatment because excessive fluid accumulation can result in serious conditions such as pleural effusion and ascites. This monitoring is crucial for patient management because it allows healthcare providers to address any fluid balance issues promptly, potentially altering the treatment plan if necessary to mitigate the risks of fluid overload.

In the case of other options, while they may have their own side effects, such as peripheral neuropathy with Vincristine or different toxicities associated with Cyclophosphamide, they are not specifically associated with significant fluid retention in the same way Docetaxel is. Thus, careful monitoring of fluid status is particularly emphasized when using Docetaxel.