Macrophages which are part of the immune system may sometimes help tumors according to this article:
http://www.cancer.gov/ncicancerbulletin/090611/page6
This may not be relevant for synovial sarcoma according to the following study (although it only looked at 7 synovial sarcoma tumor samples):
http://clincancerres.aacrjournals.org/content/14/5/1423.full