I knew that I wanted to go into cancer research after undergrad, but was stuck between choosing one of my offers for biomedical sciences or UCL's cancer biomedicine course. I was wary about specialising so soon, but it's honestly fine. In first year, we do all modules (except cancer medicine in society) with all other courses in the faculty of medical sciences, so you cover all foundations you need in general physiology (i.e you don't really specialise at all). Second and third year modules see you specialising a bit more, but in any other biomedicine course you would also be picking modules and starting to narrow your interests down anyway so I don't see it as restrictive, as long as you have an interest in learning about cancer biology. The shared first year means that they're very flexible with allowing you to switch between any medical sciences courses, so if you decided at any point in first year that you wanted to not learn about cancer specifically anymore then you could switch to applied medical sciences for example. Studying in the Cancer Institute department is really amazing as the staff who teach you work in research or as clinicians, so their careers advice and teaching is so valuable.
A typical week would be: 2 hour lab on Monday, 3 hour lecture on Tuesday, 2 hour lecture and 1 hour small group teaching on Thursday, 3 hour lecture on Friday. For this course you have to do a lot of independent lecture prep though (the content is basically taught to you online in videos and quizzes, then the lecture is building on what you've learnt by applying knowledge to clinical cases or questions and allowing you to ask questions to the professors). You have lots of free time for societies as well so you can explore other academic or extracurricular interests very easily.