Tavolini et al. used immunohistochemical staining of placental alkaline phosphatase (PLAP) on fine-needle aspirates from 57 pairs of undescended testes; six patients had positive staining. During the follow-up, one patient with negative staining developed testicular germ cell tumour (GCT) whereas none of the PLAP-positive patients did so. The authors explained their observations by an inconstant relationship between carcinoma in situ (CIS) and the development of invasive GCT, and by geographical variation of the incidence of GCT.
Undisputedly, PLAP stains positively in almost all cases with CIS, but this is not equivalent to the concept that conversely, no other cells in the testicle can stain positively for this marker. In 1998, we first reported that PLAP-positive staining could be found in about a fifth of cases with normal spermatogenesis . In a histological study of testicular biopsy specimens of 1388 presumably healthy men we found that all of the six with CIS (TIN) had positive staining of PLAP. Surprisingly, 212 other (not CIS) cases showed some positive staining of PLAP, mainly in spermatocytes and spermatogonia (Linke and Loy, unpublished). So clearly, PLAP staining is extremely helpful in diagnosing CIS, but the diagnosis must not rest on PLAP staining alone. Obviously, the authors had the misconception that all cells staining with PLAP necessarily represent CIS cells.
The authors reported a rate of 10.5% of PLAP-positive staining and they prematurely equate this finding with a corresponding prevalence of CIS in their patients. However, from a recent meta-analysis it is known that <5% of undescended testis will progress to GCT . It is disturbing that the authors uncritically did not consider methodological problems of their investigation to account for this huge discrepancy. Instead, they questioned the well-accepted relationship of CIS and GCT.
Thus regrettably, the conclusions of this paper are inappropriate and quite misleading. Probably, the most important lesson of this report is that fine-needle aspiration is not feasible in diagnosing CIS. Finally, we re-emphasize that according to current guidelines, a thorough morphological examination of testicular biopsy specimens is indispensable in diagnosing CIS (TIN). Intact seminiferous tubules are essential for an accurate morphological assessment of cells under suspicion of representing CIS. Immunohistochemical staining of PLAP or other immunohistochemical markers might be used as an adjunct .