For HER2 testing, what fixation duration is recommended for tissue samples?

• A. No less than 6 hours and no more than 48 hours
• B. 12 to 24 hours
• C. 2 to 6 hours
• D. 24 to 72 hours

Answer: (A)

Fixation duration is about getting the tissue fixed long enough for reliable antigen preservation without overdoing it. When tissue is fixed in formalin, proteins cross-link to stabilize the tissue so antibodies can bind properly during HER2 testing. If fixation is too short, epitopes may not be well preserved, leading to weak or inconsistent staining. If fixation is too long, epitopes can become masked, making staining unreliable or shifting interpretation.

Guidelines specify a practical balance: fix tissue in 10% neutral buffered formalin for six hours up to forty-eight hours. This window supports solid antigen preservation for both HER2 immunohistochemistry and FISH testing. The range that starts at six hours and ends at forty-eight hours directly aligns with the goal of dependable, reproducible results. Options that propose shorter durations (e.g., two to six hours) risk under-fixation, while longer durations (e.g., twenty-four to seventy-two hours) risk over-fixation and masking of epitopes. Although a middle range like twelve to twenty-four hours can be acceptable, the standard recommended window is six to forty-eight hours, making the sixth-to-fortieth-eight-hour range the most appropriate choice.