<s>[INST] I just noticed a purple/yellow circular bruise on my right upper arm with a while lump in the middle...feels like the size of a pea.  The entire bruise is about the size of a quarter.  It doesnt hurt!  I know it is not a bug bite, no shots and nobody has grabbed my upper arm.  What could this be?  My Grandmother on my Dads side had breast cancer. [/INST] Hi, Dear,thanks for the query to Chat Doctor virtual Clinic. I studied your query and understood your health concerns. The worry of the lump on your right upper arm, is only due to the fear of it being cancer, as your grandma had breast cancer. I reassure you, after studying the details of your query, that you should not worry about possibility of cancer in your right upper arm. Your lump appears to be an unknown insect bite. Possibility of it being boiled or sebaceous cyst is not there as the history is short. Hope this would resolve your query. Welcome for any further query in this regard. Write good review and hit thanks, if this reply helps you. Have a good day. Chat Doctor. N. </s>