Most Commons "Cancerous" G1 Ponies....

[tuneful87]

I'm just happy none of the Candy Canes and Perfume Puffs (my favorites!) are prone to cancer!

[Mermaid]

Ohhh I forgot about pinwheel and starflower! Ugh! What a nightmare to find a mint version of them!

[applejackbunny]

Starshine and Peachy in my experience 

[Jennifer2004]

Most of mine have already been mentioned, Quarterback, Sweet Stuff, etc.

But one I don't think has been mentioned that I can't seem to find without cancer is Baby Fifi. Maybe it's just my bad luck.

~Jennifer

[MiRaja]

Yeah, Gingerbread is bad.  My Gingerbread has no splotches but then I paid through the nose for her( and would charge what I paid for her if ever I were to sell her! ).

I've yet to find a Quackers in similar condition.  They're wrecky too.  But Bosenberry Pie is bad too. 

[hathorcat]

Hands down German Starshine...I think I have seen maybe a half dozen over the years without issues and every other one seems to have the start of some kind of age marks.

[zora]

german nightlight and ger starshine :[

[Beth3346]

For me Baby Buttons has been so hard to find without cancer.  She's still cute though