Is colon cancer stage 3b pt4a pn1c, no lymph nodes involvement curable?

Yes: Stage 3b usually means lymph nodes are involved, so i think your information might not be entirely accurate. However, even stage 3b colon cancer can be treated with surgery and chemotherapy and the chances of cure are good.

Discussion needed: Stage iii colon cancer does have a well defined 5-year survival rate with appropriate chemotherapy. However the chances that there is tumor spread are there, and close follow up needs to be done. These are all discussion that should really be held with your surgeon or oncologist.