T.C.
This my opinion and I am not sure I am correct in saying this so please do not take me for my word!
I would think since all turned out well and that is why you are able to make the choice to get a second opinion then probably no, you can not sue. Yes, it COULD have cost both of your lives but since you got a second opinion and they found that it was malignant as well as aggressive you had it immediately removed and appropriate treatment.
Also, what trauma did having the wrong diagnosis cause? I think finding out that you have cancer period is traumatic! I just made 7 years cancer free and I am still traumatized by the whole thing so I know where you are coming from! The whole thing is very very scary! Did waiting for the second opinion change the results any?
Personally, if it is not for the money, then I would say put it in the past and let it go! You are blessed to be alive and considered cancer free which you already know! I really do not think if you were to file a law suit that it would go anywhere. I may consider not paying for the first diagnosis since it was wrong and if you already have then maybe ask for your money back- of course you will hear then that nothing is guaranteed and medicine is a practice blah blah blah! I guess for a perfectly correct answer I would call a few lawyers- be careful though since some will give you the run around... no offense to any on here... I am still looking for an honest personal injury attorney!
What ever you do decide I wish you lots of luck! I hope you continue to thank God everyday for giving you the intuition to follow your gut and seek out a second opinion! Many blessings to you and yours for a healthy future!