The reliability of a second biopsy for determining residual tumor

Background: Often after biopsy a skin cancer appears to resolve clinically and a repeat biopsy may be done on the area in question before proceeding with further treatment. Objective: Our purpose was to assess the value of a subsequent biopsy in the treatment of skin cancers previously diagnosed by biopsy results. Methods: The results of a subsequent biopsy were compared with the results of Mohs micrographic surgery in 291 patients with biopsy-established basal cell carcinoma and squamous cell carcinoma. Pre-Mohs surgery curettings were examined in 60 of these patients to evaluate whether these could have caused false-negative Mohs results. Results: One hundred nineteen patients had a negative second biopsy, of which 75 (63%) had residual tumor at surgery. Eight of 60 patients in whom the curettings were examined had negative results from both biopsy and Mohs surgery; tumor in the curettings was shown in six of these eight patients (75%). Conclusion: This study suggests that 63% or more of subsequent biopsy specimens for skin cancer may yield false-negative results and casts doubt on the usefulness of a subsequent biopsy before surgery.