lymphoma can sometimes have a rash.
other symptoms can include fatigue, itchiness, enlarged lymph nodes, weight loss, fevers, chills, night sweats, hot flashes.
usually the way these things work is that one of two things happen. if the problem goes away in a month or so, and does not recur, nothing further is usually done. if the problem does not resolve with time and treatment, or if it resolved but recurs, a biopsy is done and a tissue diagnosis is made.