Effect of formalin fixation on tumour size and margins in head and neck cancer specimens

OBJECTIVES: To quantify tumour size and margin shrinkage due to formalin fixation in head and neck cancer specimens and determine its effect on tumour staging and margin clearance. METHODS: Tumour specimens were measured immediate post-resection and at 24 hours after fixation. Tumour was measured in 2 dimensions and one margin was measured. Shrinkage was categorised as < 10%, 10-20%, and > 20%. Effect of shrinkage on tumour stage and margin clearance were evaluated. RESULTS: A total of 50 specimens were analysed. The tumour AP (Anterior Posterior) and SI (Superior Inferior) measurements showed significant shrinkage with a mean difference of 22.93% and 21.69% respectively. > 20% shrinkage was noted in 78% of AP and 58% of SI measurements. Margins showed a mean difference of 25.61%. 84% of margins demonstrated > 20% shrinkage. In all, 46.7% of T3 and 23% of T2 tumours pre-fixation were downstaged to T2 and T1, respectively, post-fixation. CONCLUSIONS: Formalin fixation alone can be responsible for significant shrinkage of tumour and margin dimensions in head and neck specimens. It is suggested that decisions regarding the treatment plan should be made on clinical staging of primary tumour rather than pathological staging. In addition, post-excision pre-fixation margins should be considered for treatment planning.