Can subcutaneous nodules(around 1 cm) on lower legs that slightly itch wid little swelling and blackening(purplish)of skin on legs be signs of cancer?

Let's biopsy: I'm actually more concerned about a cryoglobulin or leukocytoclastic vasculitis. If you have been offered a biopsy, by all means go for it. This does not sound like erythema nodosum, but i've learned not to try to second-guess a rash / skin eruption without seeing it.

Yes: They are probably not cancer but certainly could be. You should have this checked out by your physician. If you have problems with your immune system, there is a type of cancer called kaposi's sarcoma that can look like this.

See your doc: Any new skin lesions should be brought to the attention of your friendly dermatologist.