You're simply wrong. Again, cancer is malignant by definition. And again, you seem to be confusing "cancer" with "tumor" -- your description applies to the latter, not the former.
You can label a slow-growing tumor as "not-cancer" if you want, for psychological reasons, I guess; "cancer" just sounds scarier. Some slow-growing "not-cancer" tumors are faster than others. It's a sliding scale, not a dichotomy.