Fibroadenoma or Phyllodes Tumor?? Please help

Hello,
I'm 25 years old, just came back from dr's. office. My ultrasound came back as BIRAD 4a, low suspicion, abnormality. Previous to that, I had an ultrasound at a different location, and it came out as BIRAD 3. Now, the doctor said they want to do the biopsy, which I agree with, to determine whether I have Fibroadenoma which is benigh, or ap ossible Phyllodes tumor.  The mass is 4.3 cm wide. When the doctor walked into the examining room, she merely said "oh, it's benign fibroadenoma', but when I got my copy of the rad. report, it said " Mass 4.3 cm, hypoechoic, which could be giant fibroadenoma or phyllodes tumor, core biopsy recommended".
I'm really freaked out. I know that phyllodes tumor can be benign or malignant, and that it's really rare, but I'm still freaking out. Anyone out there has any advice, experience that can help? What are the chances that it will actually be a phyllodes tumor? I mean, no matter what, the doctor said they will have a surgery to take it out because it's so big, but I have to wait two weeks until my biopsy, and I'm going insane thinking about this. Please help.
thank you!!

[japdip]

To speculate would be almost a guess in the dark. If this grew fairly rapidly and I'm assuming it did I would be thinking Fibroadenoma also. You are in agreement with the biopsy so I don't see why you would be freaking out so much. Why not just do an Excisional Biopsy and have it all done at one time since you indicate that removal will be done in any event. You are correct it is quite large .... I'm curious as to how long you have have this mass.   Regards ....

[Ina522]

I've noticed first around april of 2007. I did an ultrasound back then,and the results were benign ( birad 2), so I didn't give it more thought. Supposedly, it measured the same (4.3 cm) back in 2007 as it did in May of 2009.  My doctor said that the biopsy goes first so that they know exaclty what they're dealing with, and then surgery afterwards. I didn't ask about doing it all at once, but her exact words were "we want to know what it is we're removing" and that's what worries me much. I've read different statistics about 'rarity' of this phyllodes tumor, and that it's rare, but I'm still nervous, and waiting for two weeks is killing me.
Do fibroadenomas also grow rapidly like this phyllodes tumor? It says that the tumor is aggressive and it grows fast, but I am not sure about adenoma. Would they be able to see on ultrasound if it is malignant? I know it's hard to distinguish between adonema and phyllodes tumor, but if either was malignant, would ultrasound show that somehow?
Thank you, I appreciate it!