It’s not so straightforward if we’ll look into the LOINC files.
Indeed, when LOINC LA15460-1 ‘IV’ concept becomes a part of LL4442-1 answer list, it has displaytext (the answer string) = ‘IV’ and SubsequentTextPrompt = ‘Melanoma invades reticular dermis’. By LOINC specs, SubsequentTextPrompt is the text associated with answers such as “Other” that indicates what extra information the user should enter, for example, “Please specify:”
When we look into the details of the same LOINC LA15460-1 ‘IV’ concept when it’s a part of LL1685-8 answer list, it has displaytext = ‘IV’ and SubsequentTextPrompt = ‘NULL’. The only concept that uses this answer list is 67213-9 Stage only [PhenX] and it’s not in the area of tumor invasion.
The most representative thing for LOINC LA15460-1 ‘IV’ concept is LL10401-8 answer list where ‘IV’ means an intravenous route of administration.
This is how LOINC question/answer and most of the post-coordinated stuff build: the only thing that determines the meaning of the concept is its description and vertical hierarchical relationships. Once it matches the context, we can use it. LOINC doesn’t provide such relationships for answers (making just syntactical string equivalents of them), but SNOMED does. E.g. SNOMED 4125539 ‘IV’ concept is a Roman numeral so definitely might not be used for intravenous immunoglobulin.
Opposite stuff is SNOMED pre-coordinated concepts, e.g. 40481923 ‘pT1b category’ that implies the result of tumor pathology finding measured using TNM. Such concepts are not used as values, they are sufficient by themselves.
This is definitely what should be introduced, but we’re just at the beginning of a long walk. You already see how LOINC is good in this. A lot of other issues are still to be addressed:
- selection of Standard between LOINC/SNOMED/NAACCR;
- replacement of LOINC concepts in answer lists by another Standard or not;
- value completeness: a selection between ‘1b’ or ‘T1b’ or ‘pT1b’ or ‘pT1b stage’ or ‘pT1b tumor stage’ and accordance with Measurements of different detail degree;
- splitting of pre-coordinated concepts.
Well, the only vocab that provides all the options is NAACCR. But it has duplicates, still in the workshop and we all understand the context that goes with it. Some of the SNOMED 4152511 Roman numeral are good, but we can’t use 4152513 Upper case Roman letter here.
I really think that the above-mentioned LOINC’s and SNOMED’s mixture is a good choice at this point, but we still have nothing but NAACCR for IIIB, IVA and IVB. Let’s hear from @Christian_Reich @Dymshyts @mik @aostropolets and @mgurley what exactly to be created.
Let me try to repeat this trick 
@sbicty, @Eldar, @Sebastiaan_van_Sandi, @gregk, @larsh, @Alexandra_Orlova