I don't know who needs to hear this, but: Comms ≠ Marketing ≠ PR
I'm a scientist by training and it took me an embarrassingly long time to figure out the subtle -- but substantial! -- differences between these functions as I have transitioned from the lab to having my own comms consultancy.
Here's a **very simplified** rubric I came up with to describe the basic activites of these groups and how they overlap.
Typically, for a biotech/techbio startup, you'll want to first engage a (sci) comms specialist to help you develop your corporate and scientific narrative and apply it to your key channels (pitch deck, website, maybe social media). Then, when you are ready to make a public announcement, you'll need a Public Relations expert who can connect you to reporters and can help tailor the comms messages to get coverage. Lastly, once you are ready to engage a boarder audience (typically of customers or patients), you'll be ready to engage a marketing expert who can create things like paid social campaigns and ads to drive specific outcomes (sales, signups, clicks, etc).
Now, there are some people and agencies who do all of these functions. There are also lots of activities and similarity/differences that I didn't cover (audience and channels for two). But hopefully this is a good starting point for understanding how these functions work together to tell your company story.
Do you have other questions about comms/PR/marketing? Ask away! Do you disagree with my description of these roles? Let me know!