BMC Cancer 2008, 8:379 http://www.biomedcentral.com/1471-2407/8/379 well as smooth muscle cells of blood vessels. Eight of ten B-cell lymphomas and three of eight T-cell lymphomas were stained positively for ID2 (Table 1). tive for P16(INK4A) and also four positive for ID2. Of 51 EBV-LMP1 positive cases, 12 was negative for P16(INK4A) and 9 negative for ID2 completely. EBV-LMP1 protein was expressed in 85.0% (51 out of 60) of this group of classical Hodgkin lymphomas (Table 1). EBV-LMP1 was noted in the HRS cells, highlighting them from the complex background of lymphocytes (Figure 1C) although positive staining could also be found mini- mally or occasionally in the surrounding lymphocytes. Staining was mainly nuclear and infrequently cytoplas- mic. However, some HRS cells were negative for EBV- LMP1 staining. Three of ten B-cell lymphomas and five of eight T-cell lymphomas, but none of the ten reactive lymph nodes were stained positively for EBV-LMP1 (Table 1). P16(INK4A) protein was noted in 71.7% (43 out of 60) of the classical Hodgkin lymphomas by immunohistochem- istry (Table 1). P16(INK4A) was overexpressed mainly in the nuclei of Hodgkin and Reed-Sternberg (HRS) cells (Figure 1D). Some Hodgkin cells showed some cytoplas- mic staining of P16(INK4A) protein as well as its nuclear staining. Mummified HRS cells were often negative for P16(INK4A) protein. Many of the HRS cells with a very prominent nucleolus were positive for P16(INK4A). However, some HRS cells were negative, distinct from the positive cells nearby. Neither B nor T lymphocytes in the background of the lymphoma or other tissues showed positive staining for P16(INK4A) protein, although histi- ocytes were weakly positive. There was no P16(INK4A) staining in the lymphocytes, plasma cells and eosinophils. In the control tissues and reactive lymph nodes, histio- cytic lineage cells including macrophages, Langerhans cells, and dendritic cells were weakly positive for P16(INK4A). In the non-Hodgkin lymphomas (B-cell and T-cell lymphomas), P16(INK4A) protein was found in five out of ten B-cell lymphomas and four out of eight T- cell lymphomas, but none of lymphocytes in the reactive lymph nodes were positive (Table 1). The association between ID2 and EBV-LMP1 or P16(INK4A) Under the microscope, ID2 was detected in most EBV- LMP1 positive HRS cells, and there was a positive correla- tion between the two markers (4.400 ± 2.980 vs 4.267 ± 2.842, Rho = 0.946, P = 0.0001). However, ID2 was not correlated with P16(INK4A) in this group of Hodgkin lymphomas (4.400 ± 2.980 vs 3.567 ± 2.557, Rho = - 0.120, P = 0.191). It was also noted that HRS cells positive for EBV-LMP1 were negative for P16(INK4A) and vice versa in the same field on serial sections. The inverse cor- relation between two proteins was significant (4.267 ± 2.842 vs 3.567 ± 2.557, Rho = -0.206, P = 0.024). Among nine EBV-LMP1 totally negative tumours, four was posi- Discussion ID2 can inactivate E2A and perhaps PAX5, and recurrent chromosomal gains of the ID2 gene might contribute to the aberrant expression [19,20]. We show here that ID2 is not detectable in normal B cells but is strongly expressed in HRS cells of 83.3% of Chinese classical Hodgkin lym- phoma (50/60). These findings are in agreement with those of a previous work from Germany [14], although our ratio is slightly lower than in that report (42/42) [14]. These results suggest a possible role for ID2 in repressing B-cell-specific gene expression by inactivation of E2A and PAX5 in Hodgkin lymphoma. EBV positivity rates in clas- sical Hodgkin lymphoma vary considerably across the world [18,21-25] likely reflecting in part different patho- genesis. In our series, using EBV-LMP1 immunohisto- chemistry, we noted EBV positivity in 85.0% of cases. Other series have used in situ hybridization for EBV early RNAs (EBER) as well as EBV-LMP1 immunostaining which may explain some of the differences in EBV detec- tion rates. In our study, ID2 expression was expressed in the vast majority of classical Hodgkin lymphoma (83.3%) so it may be a potentially useful marker for identifying the HRS cell in classical Hodgkin lymphoma, independent of EBV status. In this group of Hodgkin lymphomas from China, P16(INK4A) was also overexpressed. It was found in 71.7% of the classical Hodgkin lymphomas, again, much higher than in the Malasian (49.2%) [18] but in agreement with that study it was inversely correlated with EBV-LMP1 (P < 0.05). The phenomenon supports the notion that the pathogenesis of Hodgkin lymphoma is different from that of other tumors that lose P16(INK4A). However, there may be an association with other effects of ID2 on HRS cells such as inactivation of the anti-prolifer- ative function of Rb, which could indirectly induce over- expression of P16(INK4A)[26,27]. Taken together, ID2, EBV-LMP1 and P16(INK4A) were highly expressed in HRS cells of classical Hodgkin lym- phoma, distinguishing the HRS cells from the background lymphocytes. Conclusion Our study here suggests that combined with cellular mor- phology, the three proteins could be considered as poten- tial adjunct markers to identify HRS cells in diagnosis of classical Hodgkin lymphoma. Competing interests The authors declare that they have no competing interests. Page 4 of 5 (page number not for citation purposes)