258 q 2000 Blackwell Science Ltd Cytogenetic abnormalities in PHA-stimulated lymphocytes from patients with Langerhans cell histiocytosis Susi Scappaticci, 1 Cesare Danesino, 1 Elena Rossi, 1 Catherine Klersy, 2 Gian Mario Fiori, 3 Rita Clementi, 4 Valeria Spica Russotto, 4 Grazia Bossi 4 and Maurizio Arico Á 4 and the AIEOP-Istiocitosi Group 1 Biologia Generale e Genetica Medica, Universita Á di Pavia, Pavia, 2 Servizio di Biometria ed Epidemiologia Clinic, IRCCS Policlinico San Matteo, Pavia, 3 Servizio di Oncologia, Ospedale Regionale per le Microcitemie, Cagliari, and 4 Clinica Paediatrica, IRCCS Policlinico San Matteo, Pavia, Italy Received 21 February 2000; accepted for publication 16 May 2000 Summary. The aetiopathogenesis of Langerhans cell histio- cytosis (LCH) is still undefined. Constitutional abnormalities in LCH have rarely been reported. One study showed chromosomal instability in lesional cells from three patients. No chromosomal studies are available on peripheral blood lymphocytes. Peripheral blood lymphocytes were analysed for the presence of chromatid and/or chromosomal breaks and structural rearrangements. A fluorescence in situ hybridization (FISH) painting technique was also applied in two cases. Sixteen patients with multisystem (MS, n  11) or single system (SS, n  5) LCH were studied, either at the diagnosis (n  8), during treatment (n  2) or during follow-up, when asymptomatic (n  6). Thirteen patients had chromosomal abnormalities. Eleven patients (69%) had chromatid and chromosomal breaks in 7±45% of cells. Overall, chromosome and chromatid breaks were significantly more frequent in the 11 patients with MS disease than in the five patients with SS disease: the mean percentage of cells showing chromosome and chromatid breaks was 13´4% in MS patients vs. 6´2% in SS patients (P  0´003). Chromosomal abnormalities may be found in phytohaemagglutinin (PHA)-stimulated peripheral blood lymphocytes of LCH patients at diagnosis, during the disease course and even during long-term follow-up, more fre- quently in MS disease. Chromosome instability may be considered as either a basic genetic instability or as a landmark of reaction to an environmental agent (viral?) that, through genome alteration, may play a role in histiocyte proliferation and, in some cases, also in the increased risk of malignancy. Keywords: Langerhans cell histiocytosis, chromosomal instability. Langerhans cell histiocytosis (LCH) is a rare disorder characterized by the proliferation and dissemination of histiocytes, which may cause a variable clinical pattern ranging from a single osteolytic lesion to severe dissemi- nated disease with multiorgan failure (Arico Á & Egeler, 1998). Although most cases are diagnosed during early infancy, with a peak age between 1 and 3 years (Nicholson et al, 1998), adult patients are increasingly reported (Malpas, 1998; Arico Á, 1999; Saven & Burian, 1999). The aetiology and pathogenesis are still poorly understood. An increased incidence of malignancy, solid tumours and leukaemia has been observed (Egeler et al, 1998). Although considered a sporadic disorder, rare families with multiple affected members have been reported (Arico Á et al, 1999). Cytogenetic studies demonstrating constitutional and clonal abnormalities have been reported in a few patients (Orye et al, 1982; Frost & Wiersma, 1996; Betts et al, 1998; Di Rocco et al, 1999). These findings warrant a systematic screening for the chromosomal abnormalities in patients with LCH. PATIENTS AND METHODS Patients. Only patients with biopsy proven LCH diagnosed according to current recommendations given by the Histiocyte Society (Writing Group of the Histiocyte Society, 1987; Broadbent et al, 1989) were enrolled in the study. Peripheral blood samples were collected, with informed consent, at the time of the diagnosis of LCH, before starting treatment or during the disease course, either under treatment for active disease or during follow-up when asymptomatic and off therapy. Treatment included che- motherapy according to current co-operative treatment British Journal of Haematology , 2000, 111, 258±262 Correspondence: Maurizio Arico Á, Clinica Paediatrica, IRCCS Policli- nico S.Matteo, 27100 Pavia, Italy. E-mail: aricom@unipv.it