No. Pregnancy tests are looking for a hormone in your blood and urine that is only present when you are pregnant. Some infertility treatments have this hormone in them and therefore can show up a false positive. Cancer will not. Very occasionally an ovum is fertilised but the embryo does not develop and the placenta grows out of control. This will give a very strong positive on a pregnancy test and has to be dealt with as a matter of urgency. It is called a hydatidiform mole and may (just may) develop into a cancer. Ammendum:
After only minor investigation on the subject, I was able to find documented evidence of some cancers (or their subsequent treatments) causing false positive pregnancy tests. One case study published by Tze-Kiong et al, of the Kaohsiung Medical University in Kaohsiung, Taiwan, discussed the clinical history of two female cancer patients. One patient was diagnosed with cervical cancer and the other with colon cancer. Both patients tested positive on urine pregnancy tests (based on the criterion of above-normal HCG urine levels) but otherwise were shown not to be pregnant. The article can be found on MedScape (http://www.medscape.com/viewarticle/556653). Also certain types of ovarian, uterine, and breast cancers have been shown to cause excretion of HCG in the urine. (http://www.justmommies.com/articles/false-positive-pregnancy-test.shtml) Keep in mind that tumors utilize and secrete some of the same growth factors that zygotes and fetuses do considering that both tumors and newly fertilized eggs are characterized by rapid and expansive cell replication.