Table 3.

P53: recommendations and comments from the working group.

Recommendations
A) The first method for p53 testing is represented by IHC, a widely available laboratory test, utilizing antibodies against p53. B) Genetic testing (Sanger sequencing or NGS) is indicated in case of indeterminate IHC results (disagreement or interpretative difficulties). C) Genetic testing should be carried out only in selected centers experienced in these techniques.
Comments
- Use the IHC approach for detecting p53 pattern of expression - Standardize pre-analytical and analytical protocol of testing - IHC can be performed on biopsies or surgical specimens if available, preferring the best-preserved sample as first choice
The main advantages of performing IHC on biopsies are the following:
(i) the better degree of fixation of biopsies (ii) the early knowledge of p53 status in a pre-operative setting The main advantages of performing IHC on surgical sample are the following: (i) larger amount of tumoral representative tissue; (ii) the possibility to select the best specimen for IHC testing; (iii) the possibility to overcome tumor heterogeneity. - The presence of an internal positive control is mandatory for interpretation of results. - Move to genetic testing as a confirmatory test or whenever there is any doubt in IHC interpretation.
We retain that undoubtedly diagnostic interpretative challenges by p53 immunohistochemistry are possible events, but we are also aware that equally there are similar issues around quality assurance for genetic testing of TP53 mutation (Sanger sequencing or NGS) that may not be totally reliable.