What Causes A Bruise And Lump On The Calf?

135 lbs, female, 5'8", 47 yrs.... I have no major health issues other than starting lowest dose estrogen. My issue: I noticed a dark blue vein across my outside calf area like a band recently. Just now I noticed it as a huge bruise and it seems a lump under. I do not recall hitting it on anything. I have read that skin cancer can look like a bruise. Is that true?