Merge/Consolidate data in specific columns

I have a list of patients with numbered tumor sites and I'm looking for a way to consolidate my data with entries for a third column (genotype) which remains not assigned (NA) until I receive the final results from all the hospitals within my region. The function might look like a double vertical lookup, but I'm looking for the best practice when it comes to merging that kind of data.

I'm posting the data here, because the attachment option does not show my uploaded file within the post.
===Sheet1===
Patient Tumor Genotype
PT01 1 NA
PT01 2 NA
PT02 1 NA
PT02 2 NA
PT02 3 NA
PT03 1 NA
PT04 1 NA
PT05 1 NA
PT06 1 NA
PT07 1 NA
PT07 2 NA
PT08 1 NA
PT09 1 NA
PT10 1 NA
PT10 2 NA
PT10 3 NA
PT10 4 NA
PT10 5 NA
PT10 6 NA

===Sheet2===
Patient Tumor Genotype
PT01 1 GG
PT01 2 TT
PT02 3 GG
PT03 1 TT

Originally Posted by FDibbins

I put this in D2 and copied down...
=IFERROR(INDEX(G:G,MATCH(A2&B2,INDEX($E$1:$E$5&$F$1:$F$5,0),0)),"")
was this what you wanted?

I'm looking for a function or (macro)command that replaces NA in Sheet1, column C with the correct values from Sheet2 by correctly picking (a) the patient number and (b) the right tumor number.

Originally Posted by FDibbins

So what is your expected outcome?

I haven't been successful with anything that I've tried, yet.

The final answer will look like this.

PT01 1 GG
PT01 2 TT
PT02 1 NA
PT02 2 NA
PT02 3 GG
PT03 1 TT
PT04 1 NA
PT05 1 NA
PT06 1 NA
PT07 1 NA
PT07 2 NA
PT08 1 NA
PT09 1 NA
PT10 1 NA
PT10 2 NA
PT10 3 NA
PT10 4 NA
PT10 5 NA
PT10 6 NA

I'm essentially looking for a method for replacing specific cells by reading columns 1 and 2. Changes will happen over a period of time as some hospitals take time to provide me with the results, so I would prefer that "NA" cells with no entries on Sheet2, to be left unchanged. If Visual Basic code is the only solution I'd like to see your suggestion, assuming that the code could be easily adjusted for more columns in the future.

Note that the data I provide is totally fictional. The real database contains 22000 entries but I am not allowed to share it.

I've tried it but it didn't work.