Possible Endometrial cancer. Endometrial biopsy normal. Hysteroscopy D&C recommended because lining is 15. What is this suspect of?

Endometrial polyp. If the biopsy was negative, chances are minimal that you have cancer. Most likely, you have a polyp causing the thickened endometrium. The hysteroscopy and D&C will show what is definately going on and allow removal of the tissue. It will also confirm the biopsy results, likely showing no cancer.
Make sure. When Bx is done it takes sample from few spots....which can miss a focal disease. D& C gets all the endometrium out and gives a better chance od Dx. If superficial enough it may cure it also. Not knowing your age, disease hx, duration, reproductive hx.....this much can be said.