I haven't read the responses so forgive me if I'm repeating what's been said.
Why are you dating? Is it for fun and companionship? Or is it for marriage and a deep relationship?
If it's for fun and company, I don't think you owe a casual date any deeply personal information about yourself. I believe in being honest but you are entitled to privacy. I think if you are planning on keeping it light and fun and sparkly and just an enhancement to life and not a heavy romance with marriage at the end, then I would date without telling. Because you are right, I think many men are going to run at the idea of terminal cancer, even if you don't plan on a serious relationship. Of course, I think you should tell him that you are dating for fun and companionship only and you want to keep it light and not to get serious - but you don't have to tell him why.
On the other hand, if you are hoping for marriage and a lasting commitment, then I think you have to tell pretty early on - as soon as you suspect this is the person you want by your side. Having metastatic cancer is so BIG that you can't really have a deep relationship without the other person knowing anyway.
And then, you have to be prepared for the possibility that they will back away or be angry at your not being up front. But, you can't blame them - they have a right to choose their own future. Very few would choose a future with a terminally ill person- although some do.
Rejection? Yes, that is a legitimate fear. You are between a rock and a hard place and there is really no good perfect way to handle it. I too am Stage IV and I honestly do not think I would date anybody with advanced cancer. Maybe when I was young and romantic but now that I know what it entails, no, I wouldn't. It's just too much to deal with.
But, there are people out there who fall in love and get married with cancer every day. And, there are people with cancer who go out and have cosmopolitans and dance and have sex too, and don't think about making a future. Both are okay
.
You are pretty cute in your avatar so I bet you have a lot of offers.

__________________
http://butdoctorihatepink.com
08/17/09 Dx'd.
Multifocal/multicentric IDC, largest 3.4 cm, associated ADH, LCIS, DCIS
HER2+ ER+/PR- Grade 3, Node Negative
10/20/2009: Right mastectomy, reconstruction with TE
12/02/2009: Six rounds TCH, switched to Taxol halfway through due to neuropathy
03/31/2010: Finished chemo
05/01/2010: Began tamoxifen, the worst drug ever
11/18/2010: Reconstruction completed
12/02/2010: Finished herceptin
05/21/2011: Liver Mets. Quit Tamoxifen
06/22/2011: Navelbine/Zometa/Herceptin
10/03/2011: Liver Resection, left lobe. Microwave ablation, right lobe - going for cure!
11/26/2011: C-Diff Superbug Infection, "worst case doctor had seen in 20 years"
03/28/2012: Progression in ablated section of the liver - no more cure. Started Abraxane, continue herceptin/zometa
10/10/2012: Progression continues, started Halaven, along with herceptin and zometa.
01/15/2013: Progression continues, started Gemzar and Perjeta, an unusual combo, continuing with herceptin and zometa
03/13/2013: Quit Gemzar, body just won't handle it. Staying on herceptin, zometa and perjeta.
04/03/2013: CT shows 50% regression in tumor, so am starting back on Gemzar with dose reduction, staying with perjeta/herceptin/zometa. Can't argue with success!
05/09/2013: Discussing SBRT with Radiology due to inability of bone marrow to recover from chemo.
06/07/2013: Fiducial placement for SBRT
07/03/2013: Chemo discontinued, on Perjeta, Herceptin and Zometa alone
07/25/2013: SBRT (gamma knife) begins
08/01/2013: SBRT completed
08/15/2013: STABLE! continuing with Perjeta, Herceptin, Zometa
06/18/2014: ***** NED!!!!***** continuing with Perjeta, Herceptin, Zometa
01/29/2014: Still NED. continuing with Perjeta, Herceptin. Zometa lowered to every 3 months instead of monthly.
11/08/2015: Progression throughout abdomen and lungs. Started TDM-1, aka Kadcyla. Other meds discontinued. Remission was nice while it lasted.
5/27/18: Stable. Kadcyla put me right back in the barn. I have two teeny spots on my lungs that are metabolically inactive, and liver is clean.
I’m beating this MFer. I was 51 when this started and had two kids, 22 and 12. Now I’m 60. My oldest got married and trying to start s family. My youngesg graduates from Caltech this June. My stepdaughter gave me grandkids. Life is fantastic.