Loss of Retinoblastoma Protein Expression is Frequent in Small Cell Neuroendocrine Carcinoma of the Cervix and is Unrelated to HPV Type C, SIMON HERRINGTON, MBBS, MRCPATH, DPHBL, DAVID GRAHAM, MSc, SHIRLEYA, SOUTHERN, FIMLS, ASHWIN BRAMDEV, MBCHB, FFPATH (SA), AND RUN JAN CHETrY, MB BCH, FRC PATH (UK), DPHIL We have previously identified an inverse relationship between p53 and refinoblastoma protein (pRb) immunoreactivity in non-small cell carcinoma of the cervix. Because pRb is infrequently expressed in small cell carcinoma of the lung, we analyzed 25 small cell neuroendo- crine carcinomas of the cervix to test the hypotheses that 1) lack of pRb expression is associated with the neuroendocrine phenotype in human papillomavirus (HPV)-associated cervical carcinoma and 2) the inverse relationship between p53 and pRb immunoreactivity also occurs in these tumors. I-IPV type was analyzed by PCR, HPV distribution by in situ hybridization and expression of p53 and pRb by immunohistochemistry. All of the tumors contained HPV sequences, with 13 tumors HPV 16 positive, 11 HPV 18 positive, and 1 HPV45 positive. In situ hybridization showed large intranuclear dot-like signals in all positive tumors, suggesting viral integration. No multiple infections were identified. Expression of retinoblastoma protein was not detectable in 23 tumors (92%), the remaining two showing only weak, focal expression. Expression of p53 protein was variable in dislribution and intensity. It did not correlate with HPV type, and there was no relationship with pRb immunoreactivity. These data indicate that, although there is no reciprocal relationship between p53 and pRb immunoreactivity in these tumors, refinoblastoma protein is infrequently expressed in HPV-containing small cell neuroendocrine carcinoma of the cervix, irrespective of infecting HPV type. This is consistent with the reported findings in small cell carcinoma of the lung and suggests that the small cell neuroendocrine phenotype may be related to the abrogation of retinoblastoma protein function. HuM PATrIOL30:906-910. Copyright © 1999 by W.B. Saunders Company Key words: papillomavirus, small cell carcinoma, p53, retinoblas- toma. Abbreviatim~: HPV, human papillomavirns; pRb, refinoblastoma protein; PCR, polymerase chain reaction. Human papillomaviruses (HPV) infection is the major causative factor in cervical carcinogenesis, 1 with epidemiological evidence indicating that most cervical neoplasia is attributable to HPV. 2 More than 95 HPV types have been described, and phylogenetic analysis has identified 11 separate groups of anogenital HPVs based on their sequence homology? Analysis of clinical lesions has identified low-risk, intermediate-risk, and high-risk HPV types4 based on their relative risk associa- tions with intraepithelial and invasive squamous lesions. HPV 18 is associated particularly with invasive disease, and it has been suggested that tumors containing this viral type are more aggressive than those containing other HPV types. 5This is supported by the fact that HPV 18 is found in clinically aggressive tumor types, such as clear cell adenosquamous carcinoma6 and small cell carcinoma,v The suggestion that the neuroendocrine pheno- From the University of Liverpool, Department of Pathology, Royal Liverpool University Hospital, Liverpool, United Kingdom; and the Department of Pathology, University of Natal School of Medicine, Durban, South Africa. Accepted for publication March 29, 1999. Supported by the Universities of Liverpool and Natal. Address correspondence and reprint requests to C.S. Herring- ton, University of Liverpool, Department of Pathology, Duncan Building, Royal Liverpool University Hospital, Liverpool L69 3GA, United Kingdom. Copyright © 1999 by W.B. Saunders Company 0046-8177/99/3008-0005510.00/0 type of small cell neuroendocrine carcinoma of the cervix is associated with infection with HPV 188 is of potential biological significance. The protein products of the early genes of HPVs are capable of binding to and inactivating cell cycle control proteins, particularly p53 and the retinoblastoma protein (pRb) which bind to the E6 and E7 proteins, respectively. 9 The binding orE7 to pRb leads to abrogation of the G1/S control point and allows cells to pass directly through the restriction point into late G1 phase without a requirement for cyclin D1 expression. 1° No clear difference has been identified between the ability of HPV 16 and 18 gene products to abrogate this checkpoint. However, HPV 18 integrates more frequently into the host genome, 11 and therefore the aggressive behavior of these tumors may be related to early integration events with consequent upregulation of HPV early gene transcription and abrogation of p53 and pRb function. This suggestion is supported by reports that small cell carcinomas of the lung express pRb infrequently.12,1s However, it is not known whether this absence of pRb expression is common to small cell neuroendocrine carcinomas in other anatomic sites, including the cer- vix. We have previously identified pRb expression in most (86%) squamous cell carcinomas of the cervix and also showed an inverse relationship between p53 and pRb immunoreactivity. 14 In view of these observations, we analyzed a series of small cell neuroendocrine 906