Have had 1 swollen inguinal lymph node for 3 weeks. it is about 2cm in size, painless, but movable and has not grown. what are the chances it's cancer?

Very little: Most likely it is an enlarged node in reaction to a local infection somewhere in urogeital tract or skin. However, if it persists without a clear cause, you'll need to have it biopsied

Significant size: 2 cm node significant but depends on findings. Is there any pathology on the leg on the side of the node. Has the anal caal area been examined for cyst or any inflammatory proeess. If warm soaks are applied 2x daily to site of node and if no regression noted then bx indicated. Even though young, lymphoma can be present

Very unlikely: There are several potential causes for your symptoms, the least of which is cancer, These include irritation from shaving and sexually transmitted infections. It can also be a lipoma or hernia. Given the duration of your lump, I would recommend seeing a clinician for an examination and possible diagnostic tests. Take Care!