Hi!!! Not a transfem here but as someone who has the tumor condition described above that raises prolactin levels, I can absolutely describe the exact things that led to my diagnosis and why most people experiencing nipple discharge probably don't have this issue, and the steps that you and your doctor should take!
First off, the tumor I have is called a microedanoma. Its really small, less than 5mm wide, and it's pushing my on pituitary gland, causing it to produce more prolactin.
The way I found this out was through:
Spontaneously developing nipple discharge. Spontaneous is key here! As the posters above have mentioned, if you've recently changed medications, those should absolutely be investigated as a potential cause first. My doctor specifically asked if I'd started any new medications when I went to them with symptoms.
Physical exam. My doctor physically examined my chest, breast tissue, and glans. When they found no lumps, swelling, or anything else to suggest tumors or infection, cancer immediately became far less of a concern. This is an important step. If a doctor tries to send you for an MRI without doing even a cursory physical exam, push back on that immediately. Even if its not cancer, it could be a tumor in your breast tissue.
Blood test. My doctor sent me in for lab work, and my prolactin levels came back elevated while everything else was normal. Again, if your doctor tries to send you for an MRI before doing any blood work, PUSH BACK ON THAT. Bloodwork could also reveal any other issues or rule out certain causes. Mine was straightforward because only prolactin was raised, but if other hormones were present it could have been a lot of different things.
Breast ultrasound. My doctor was pretty sure I'd need an MRI at this point, based on symptoms and blood work, but as a final step I got a breast ultrasound done to definitively rule out cancer or infection. (As a side note, its also far more common for insurance to cover breast ultrasounds/mammograms than MRIs, so this is also a cost saving measure for the patient). No tumors or infections were found.
MRI. With a probable diagnosis and other avenues definitively cleared out (no medication changes, infections, or tumors elsewhere), I finally went in for an actual MRI. It was at this stage they found the microadenoma.
If you're like me and one of the very rare people who actually have this kind of tumor, dont worry! There's medication to both manage symptoms (nipple discharge) and manage tumor size, and they're less than 20 USD for 3 months supply. You will be okay.
If you're not like me, congrats! You don't have a tumor. That means you're likely having a weird symptom for something really common, and you should go down the list of steps described above to figure out the issue. I have a transfem friend who does not share my tumor condition but did experience nipple discharge, turned out she had an infection that wasn't discernible through physical exam but was identified through bloodwork. Bodies are weird!
Advocate for yourself! Do not pay for MRIs if you don't have to! You probably don't have a brain tumor and there's a clear path to check if you do. Your problem is almost certainly straightforward and inexpensive to solve. You got this.