P. Mukunyadzi et al., Comparison of MyoD1 immunostaining of pediatric tumors using frozen or paraffin-embedded sections, APPL IMMUNO, 7(4), 1999, pp. 260-265
Distinction of rhabdomyosarcomas (RMS) from other tumors can be difficult,
requiring use of monoclonal antibodies against unique muscle proteins. In p
revious studies using cryostat sections, we found that MyoD1, a transcripti
on factor that activates the expression of muscle-specific genes, is highly
expressed in rhabdomyosarcoma and useful in diagnosis. Recent studies usin
g paraffin sections demonstrated poorer results, leading us to compare MyoD
1 staining using dual paraffin versus frozen sections of tumor tissue. We p
erformed immunostaining on companion frozen and paraffin sections of 69 ped
iatric tumors (40 rhabdomyosarcomas and 29 putative non-rhabdomyosarcomas [
nRMS]), using similar dilutions of antiMyoD1 monoclonal antibody 5.8A. Twen
ty-four of 40 (60%) frozen rhabdomyosarcomas and 14 of 40 (35%) paraffin-em
bedded rhabdomyosarcomas were nuclear positive for MyoD1. Of the 29 putativ
e nonrhabdomyosarcomas, six of 29 (21%) and three of 29 (10%) were nuclear
positive, using frozen and paraffin sections, respectively. These positive
cases included one ectomesenchymoma, one embryonal sarcoma of liver, one ne
urofibroma, three undifferentiated sarcomas, and one Wilms' tumor. In retro
spect, these nine nuclear-positive cases appear to have myogenic potential.
In six frozen and 12 paraffin RMS sections and in nine frozen and 15 paraf
fin putative nRMS sections, only nonspecific cytoplasmic staining was obser
ved. We conclude that MyoD1 immunostaining of small round cell tumors is mo
re reliable and sensitive using frozen sections, despite its potential appl
icability in paraffin sections.