Prostate Mass in a Young Man

Specimen Type:

Prostate

History:

A 29-year-old young man underwent needle biopsies of a mass lesion in the left side of the prostate. His serum PSA level is within normal limit.

Pathologic Features:

The biopsies show diffuse sheets of small cells infiltrating prostatic fibromuscular stroma (Fig 1). Cellularity is variable, ranging from compact cellular areas to loose myxoid regions, which creates an alternating light and dark pattern (Figure 2). The cells are small with hyperchromatic nuclei and eosinophilic or clear cytolplasm (Fig 3, 6). Some tumor cells exhibit ribbon-like eosinophilic cytoplasm, and “tadpole” cells are also seen (Figure 4, 5). There are frequent mitotic figures (Figure 6). The tumor cells are positive for desmin and negative for smooth muscle actin (Figure 7, 8).

Differential Diagnosis:

  • Prostatic stromal sarcoma
  • Leiomyosarcoma
  • Prostatic stromal hyperplasia with atypia (PSHA)
  • Rhabdomyosarcoma

Prostatic stromal sarcoma: Prostatic stromal sarcoma is extremely rare, and about 20 cases have been reported (reference 1). Histologically, stromal sarcomas are markedly cellular with spindle cells arranged in a fascicular pattern, and exhibit variable degrees of cytologic atypia including nuclear enlargement and pleomorphism, and mitosis. Immunohistochemically, stromal sarcoma characteristically expresses progesterone receptor (PR); most tumors are positive for CD34 and negative for desmin, allowing them distinguished from myogenic tumors.

Prostatic stromal hyperplasia with atypia: It consists of stromal nodules in the transition zone with increased cellularity and nuclear atypia. The lesions may appear as solid stromal nodules or with atypical cells interspersed with benign glands. Stromal nuclei are large, hyperchromatic and often multinucleated or vacuolated, with inconspicuous nucleoli. There are no mitotic figures and no necrosis. Stromal hyperplasia with atypia has no malignant potential, and the atypical cells are considered degenerative.

Leiomyosarcoma: This is the most common sarcoma originating the adult prostate, accounting for 30% of all prostatic sarcomas but is rare with about 100 reported cases. Histologically, prostate leiomyosarcoma has a varied appearance ranging from spindled cell neoplasm reminiscent of smooth muscle to pleomorphic sarcoma. Epithelioid features may be present. Most tumors are immunoreactive with antibodies to vimentin and actin, and reactivity with antikeratin antibodies does not exclude the diagnosis of leiomyosarcoma. Prostate leiomyosarcoma has a poor prognosis, although the length of survival is variable. Radical surgery appears to offer the best chance for cure, although there may be a role for multimodality therapy with chemotherapy and radiotherapy.

Rhabdomyosarcoma: This is the most common prostate malignancy in children and adolescents. Less than 20 cases have been reported in adults. Unlike prostate adenocarcinoma which is classically hypoechoic, prostatic rhabdoyosarcoma is isoechoic by ultrasound. Grossly, they tend to be solid mass with a gelatinous appearance. Microscopically, most are embryonal nonbotryoid rhabdomyosarcoma with a small percentage of cases being of the alveolar subtype. The embryonal subtype is composed of diffuse sheets or nests of small hypechromatic cells with a moderate amount of eosinophilic cytoplasm. Condensation of cells along protrusions into adjacent cavities can create the compact “cambium layer”. Cytologically, “tadpole” and ribbon-like “strap” cells that have cross-striations indicative of skeletal muscle lineage can be seen. Alveolar subtype is of high grade with pleomorphic, hyperchromatic nuclei, coarse chromatin, and numerous mitotic figures.

Diagnosis:

Embryonal rhabdomyosarcoma of the prostate

Key features:

  • Histologically, small rounded or elongated cells, arranged in diffuse sheets or nests; cellularity is variable, ranging from compact cellular areas to loose myxoid regions.
  • Cytologically, there is a range of differentiation, from primitive stellate cells to “tadpole” and ribbon-like “strap” cells that have cross-striations.
  • Immunohistochemically, positivity for vimentin, muscle-specific actin, and desmin.

Comment: The case presented here is a follow-up case in which a conclusive diagnosis cannot be rendered in the previous biopsy due to limited material. Diagnosis of rhabdomyosarcoma can be challenging when a small tissue sample in a biopsy specimen is encountered. Identification of typical “tadpole” or ribbon-like “strap” cells is diagnostic. However, this feature can be present very focally in some cases. Presence of compact areas alternating with loose myxoid regions, creating light and dark pattern, provides another clue. Rhabdomyosarcoma may be difficult to distinguish from leiomyosarcoma or stromal sarcoma of the prostate. Unlike stromal sarcomas, which often contain scattered normal prostatic glands, rhabdomyosarcomas are devoid of prostatic glands except at the interface between tumor and normal adjacent prostatic tissue. Rhabdomyosarcoma is less likely to express CD34 than stromal sarcoma, and fails to express smooth muscle actin (SMA) unlike leiomyosarcoma which stains positively for SMA.

Rhabdomyosarcoma of prostate is extremely rare in adults. Multimodal therapy, including surgery, chemotherapy, and radiation has improved outcome in children, whereas in adults the prognosis is poor.

References:

  1. Chang YS, Chuang CK, Ng KF, et al. Prostatic stromal sarcoma in a young adult: a case report. Arch Androl. 2005 Nov-Dec;51(6):419-24.
  2. Cheville JC, Dundore PA, Nascimento AG, Meneses M, Kleer E, Farrow GM, Bostwick DG. Leiomyosarcoma of the prostate. Report of 23 cases. Cancer. 1995 Oct 15;76(8):1422-7.
  3. Nabi G, Dinda AK, Dogra PN. Primary embryonal rhabdomyosarcoma of prostate in adults: diagnosis and management. Int Urol Nephrol. 2002-2003;34(4):531-4.
  4. King DG, Finney RP. Embryonal rhabdomyosarcoma of the prostate. J Urol. 1977 Jan;117(1):88-90.
  5. Hossain D, Miers I, Mclennan GT, Bostwick DG : Prostatic Stromal Hyperplasia with atypia : A follow up study of 10 cases. Arch. Pathol. Lab. Med (in press)