How does kaposi's sarcoma and normal leg abrasion differ from one another?

See picture: Kaposi's sarcoma: "the tumors most often appear as bluish-red or purple bumps on the skin". Abrasion is superficial scrapings of(damage to )the skin.

Kaposi's is an: (human herpes virus 8) associated vascular malignancy that can be widespread in men infected with progressive HIV disease. It is not associated with trauma, as abrasions would be, does not change colors and fade away like abrasions would be and looking at them have a much more defined edge than an abrasion does.