Can hard subcutaneous nodules(around 1 cm each)on lower legs, that slightly itch and blackened skin and slight swelling of legs be symptoms of cancer?

There are many: Types of cancer but in your age group i would not jump to that conclusion? You likely had two sebaceous cysts or someting benign. Get seen but cancer is very low probability. Good luck.

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.