HMGA2 immunostaining is a straightforward technique which helps to distinguish pulmonary fat-forming lesions from normal adipose tissue in small biopsies: a retrospective observational study about a series of 13 lung biopsies

BACKGROUND: A tracheobronchial lesion observed during an endoscopic examination is usually sampled by the pulmonologist and sent to the pathologist for microscopic examination. Adipocytes may be observed in the lamina propria of tracheobronchial biopsies, which may complicate diagnosis of sampled lesions because these adipose cells may be part of the lesion (lipoma or pulmonary hamartoma), but may also be a normal component of the bronchial mucosa. Because endoscopic samples frequently miss their target, adipocytes observed in such biopsies usually lead to uncertainty regarding diagnosis. Both pulmonary hamartomas and lipomas have a high frequency of translocations involving HMGA2, resulting in over expression of the fusion protein. The literature suggests that only 31% of tracheobronchial lipomas are correctly diagnosed on biopsy, sometimes leading to unnecessary aggressive surgical resection. METHODS: We performed retrospective study of tracheo-bronchial biopsies containing adipocytes using HMGA2 immunostaining in order to define their nature and to assess the diagnostic utility of this marker. RESULTS: In total, 13 lesions biopsied in 12 patients and containing adipocytes were immunostained for HMGA2. Nuclear immunostaining was detected in 7 out of the 13 lesions (54%), allowing us to diagnose a lipoma or hamartoma. CONCLUSION: HMGA2 immunostaining is an affordable and straightforward technique for accurate description of biopsies containing adipose cells. When positive, a diagnosis of benign adipose lesion can be made with confidence since well-differentiated liposarcomas have never been described in the tracheobronchial tree. Our work enabled us to diagnose a benign adipose lesion in 54% of cases, above the rate of 31% reported in the literature, based solely on morphological analysis. Overall, HMGA2 immunostaining could help pathologists to provide accurate diagnosis of tracheobronchial adipose lesions, leading to conservative treatment, for the overall benefit of patients.