ROS1 pattern of immunostaining in 11 cases of spitzoid tumour: comparison with histopathological, fluorescence in-situ hybridisation and next-generation sequencing analysis.

AIMS: Spitzoid tumours have been shown to harbour exclusive kinase fusions. Few studies have analysed substantial numbers of ROS1-rearranged lesions. The aim of the present study was to investigate also their immunohistochemical profile. METHODS AND RESULTS: Among a group of 35 spitzoid tumours, of which 34 were consecutively diagnosed in a 3-year period, we found 11 ROS1 cases that were immunohistochemically positive, from 10 patients, eight of whom were female and two of whom were male, and who were aged 3-52 years (median, 29 years); most lesions (eight) were localized on the lower extremities. Four patterns of immunostaining were observed: cytoplasmic granular diffuse (six cases), sparse cytoplasmic granules (three cases), paranuclear dots (one case), and nuclear (one case). Fluorescence in-situ hybridisation (FISH) analysis showed all cases to be rearranged (cut-off of >15%). RNA next-generation sequencing (NGS) analysis showed specific fusions of ROS1 in four cases: two with PWWP2A, one with PPFIBP1, and one with ZCCHC8. DNA NGS analysis showed in five cases, specific mutations of AKT, EGFR, NRAS, MYC, ALK, and KIT. ROS1 lesions belonged predominantly to the 'atypical Spitz tumour' group, and showed mainly a nested histological pattern. Interestingly, one patient developed two ROS1-positive lesions. CONCLUSIONS: Immunohistochemistry showed 100% sensitivity and specificity as compared with the FISH results, corresponding to ROS1 rearrangement in 31% of cases studied. These observations shed new light on the value of immunohistochemical evaluation of ROS1 in spitzoid tumours. ROS1 patterns of immunostaining probably reflect different subcellular localisations of ROS1 fusions, although no specific correlations were found in the cases studied. Immunohistochemistry and FISH were the most sensitive techniques for detecting ROS1 rearrangement in this subset of neoplasms.

Alveolar rhabdomyosarcoma of the uterine cervix. A case report confirmed by FKHR break-apart rearrangement using a fluorescence in situ hybridization probe on paraffin-embedded tissues.

Alveolar rhabdomyosarcoma (ARMS) is a very rare malignant soft tissue tumor found in the uterine cervix. In fact, to our knowledge, only 3 cases have previously been described in the literature. A 49-year-old premenopausal woman who had a history of vaginal bleeding underwent hysterectomy for multiple uterine nodules. Pathologic examination showed multiple leiomyomas in the uterus and ARMS in the cervix. An FKHR break-apart rearrangement by fluorescence in situ hybridization (FISH) probe on paraffin-embedded tissues identified specific chromosomal abnormalities. Systemic chemotherapy and pelvic irradiation were also performed. She remains in clinical remission from neoplastic recurrences 14 months after surgery. The literature has been reviewed; the histologic differential diagnosis of this rare lesion has been discussed and FISH has been suggested to be useful in differentiating ARMS from other poorly differentiated round cell tumors.