—  SHORT COURSE #21  —

Mesenchymal Neoplasms of the Female Genital Tract

Case 1 - Embryonal Rhabdomyosarcoma

Teri Longacre, Esther Oliva and Robert Soslow


Introduction
Rhabdomyosarcoma (RMS) is a malignant neoplasm originating from myogenic progenitors cells that show variable stages of skeletal muscle differentiation. RMS is the most common soft tissue tumor found in children, accounting for less than 10% of all pediatric solid tumors. Approximately 20% of pediatric RMSs originate in the genital tract, making this the second most common site. Soft tissue sarcomas in the adult population account for 1% of adult malignancies, and RMS accounts for only a small fraction of these tumors. Although childhood RMS has a predilection for the genitourinary system, this is not the case for adults, making RMS of the adult female genital tract an extremely rare tumor [1, 2, 3] .

RMS may be categorized into three major variants with significant differences in clinical behavior and prognosis. The most common and generally most favorable variant is embryonal RMS, which encompasses botryoid, spindle cell, and anaplastic histologic subtypes. The recently described sclerosing RMS subtype [4] may also be related to the embryonal tumors. The other less common histologic variants include alveolar and pleomorphic RMS, which are usually associated with a significantly poorer clinical outcome. Identification of the clonal chromosomal translocations t(2;13)(q35;q14), involving the PAX3-FKHR fusion, and t(1;13) (p36;q14), involving the PAX7-FKHR fusion, plays an important role in the etiology, diagnosis and prognosis of alveolar rhabdomyosarcoma.

Botryoid embryonal rhabdomyosarcoma is the most common RMS subtype in the female genital tract. Rare examples of vulvar alveolar rhabdomyosarcoma [5] and spindle cell rhabdomyosarcoma [6] have been reported. Most of the clinical and pathologic data that have been collected on RMS have been through cooperative group trials looking at multimodality treatment for pediatric RMS at multiple anatomic locations, including the female genital tract [7, 8, 9, 10, 11, 12]. The case selected for discussion is very unusual in that the patient is an adult.

Clinical Features
Our group studied the clinical features of adults with rhabdomyosarcomas of the female genital tract [13]. The median age at diagnosis was 48 years (range, 16–69) and the most common presenting symptom was abnormal vaginal bleeding, which included post menopausal bleeding and menometrorrhagia in premenopausal women. The majority of women presented with locoregional disease. Ten women (71%) presented with FIGO stage I/II disease, and 12 (86%) presented with IRSG classification I–III disease. The average size of the tumors at presentation was 34 mm (range, 8–60 mm).

The primary site of disease was the cervix in 8 women (53%), making it the most common. The other sites included uterine corpus, 3 (20%); vulva, 2 (13%); fallopian tube, 1 (7%); and ovary, 1 (7%). In this adult population, none of the tumors originated in the vagina. There were 11 (73%) embryonal RMSs, and 8 (73%) of these had classic botryoid features. The other histologic subtypes included 2 (13%) pleomorphic and 2 (13%) alveolar. All cervical lesions were embryonal, and both vulvar lesions were of alveolar histology. There was no distinct pattern of distribution of histologic subtypes at the other gynecologic sites. The majority (80%) of women with embryonal RMS presented with early-stage disease (Intergroup Rhabdomyosarcoma Studies [IRSG] group I); in comparison, 75% of women with non-embryonal RMS presented with advanced-stage disease (IRSG group III/IV).

For the entire cohort, the median time to progression was only 9 months and the median disease specific survival was 21 months. The 2-year progression free survival was 15% and the 5-year disease specific survival was 29%. Neither age nor stage correlated with survival. Women with a cervical primary RMS had a significantly increased time to progression compared to women with disease at other gynecologic sites. In addition, women with an embryonal histologic variant had significantly improved progression free survival compared to non-embryonal variants. These survival statistics contrasted sharply with the historically rather positive survival rates in pediatric RMS: 5-year overall survival of 82% compared with 66% for non-embryonal variants and 5-year survival rates of 94% for the botryoid histologic subtype specifically [14, 15]. Most adult patients have been treated surgically, with or without chemotherapy and radiation therapy. They have not, for the most part, been treated with regimens used in children, where primary surgical management is very uncommon. This may contribute to some of the survival differences noted.

Morphology
Botryoid rhabdomyosarcomas are polypoid tumors with a densely cellular zone of primitive cells in a subepithelial distribution (cambium layer) [16]. The substance of the polyps is generally myxoid or edematous, with varying cellularity. The lesional cells are rhabdomyoblasts, which have assorted appearances, ranging from small, round, blue and undifferentiated, to strap-shaped, with eosinophilic cytoplasm and easily appreciated cross striations. Interestingly, cartilaginous differentiation is found in a significant minority of cases.

The non-polypoid and infiltrative portions of botryoid rhabdomyosarcomas are histologically indistinguishable from embryonal rhabdomyosarcomas of the usual (non-botryoid) sort. There are commonly cellular zones that contrast with paucicellular zones containing myxoid or edematous matrix. Rarely, cambium layers are found cuffing non-neoplastic endocervical glandular clefts. Like botryoid tumors, these sarcomas contain mixtures of rhabdomyoblasts in different stages of differentiation. Round and spindled cells with brightly eosinophilic cytoplasm are present in nearly every case and are important clues to the diagnosis.

Immunohistochemistry
The typical immunophenotype includes expression of desmin, muscle-specific actin, myogenin and Myo-D1. These markers are found in 90-100% of RMSs (they are sensitive markers [17, 18, 19, 20] ), but desmin and muscle-specific actin are certainly not specific, as they are commonly found in tissues demonstrating smooth muscle and myofibroblastic differentiation. Myogenin and Myo-D1 are regulatory proteins expressed early in skeletal muscle differentiation and show nuclear localization. In general, the expression of these markers is negatively correlated with differentiation, such that only scattered myogenin positive cells are found in embryonal rhabdomyosarcomas lacking strap cells. According to the recent publication of Morotti and colleagues [21], only 2-3% of rhabdomyosarcomas lacked Myo-D1 or myogenin expression—but all of these samples had been subjected to fixation in B5. Expression of myogenin and Myo-D1 is common to all tumors demonstrating skeletal muscle differentiation, which means that tumors other than rhabdomyosarcoma (e.g. carcinosarcoma containing rhabdomyoblasts) should be excluded before using myogenin immunoreactivity alone to make a confident diagnosis of rhabdomyosarcoma. Morotti's study [21] highlighted the specificity of these markers, reporting expression limited to tumors containing rhabdomyoblasts (RMBs). These included not only rhabdomyosarcomas, but also Wilms tumor containing RMBs, germ cell tumors with RMBs and pleuropulmonary blastoma. Tumors frequently confused with the spindle cell variant of rhabdomyosarcoma, congenital infantile fibrosarcoma, desmoid tumors and myofibromatosis, were negative for these markers. It should be also be pointed out that small numbers of RMSs have been described to express markers such as CD99 (O13), cytokeratin, S100 and WT1, markers more commonly expressed in histologic mimics of RMS.

Differential Diagnosis
The histologic differential diagnosis of embryonal rhabdomyosarcoma in the gynecologic tract in adults includes mesodermal stromal polyp, genital rhabdomyoma, leiomyosarcoma, and vaginal, cervical and uterine neoplasms that may contain rhabdomyoblasts; these include adenosarcoma [22, 23, 24], carcinosarcoma and, unusually, endometrial stromal sarcoma [25]. The extent of skeletal muscle differentiation in these tumors may be such that isolated microscopic fields are indistinguishable from rhabdomyosarcoma. Very rarely encountered sarcomas in this region include alveolar soft part sarcoma, Ewing sarcoma/peripheral primitive neuroectodermal tumor (PNET) and malignant peripheral nerve sheath tumor [26].

Mesodermal stromal polyp vs embryonal rhabdomyosarcoma
Mesodermal stromal polyps, also referred to as fibroepithelial stromal polyps or vaginal polyps, are benign polyps that usually occur in the vagina and are commonly diagnosed during pregnancy. Unusual sites of occurrence include cervix, vulva [25], and even endometrium [28]. Most polyps contain an edematous or myxoid ground substance with the type of thick-walled vessels commonly found in usual endocervical or endometrial polyps. The predominant lesional cell is spindle shaped, although there is typically an admixture of cells with a single ovoid nucleus or multiple rounded, hyperchromatic and smudged nuclei arranged in wreaths. Although there is no well-defined Grenz zone between the polyp's stroma and the overlying epithelium, a cambium layer of the sort seen in embryonal rhabdomyosarcoma is not observed. It should not be difficult to find desmin, ER, PR [29] and smooth muscle actin immunoreactivity in these lesions, but myogenin and myo-D1 expression should not be encountered. Unusually and particularly during pregnancy, mesodermal stromal polyps can show hypercellularity, marked pleomorphism and significant mitotic activity (more than 10 mitotic figures per 10 high power fields) [27]. The absence of a cambium layer and rhabdomyoblasts that express myogenin in a pregnant patient with a vaginal polyp would be against rhabdomyosarcoma, although other sarcomas and pseudosarcomatous tumors should be considered.

Genital rhabdomyoma vs embryonal rhabdomyosarcoma
Genital rhabdomyomas are extremely rare proliferations that have been reported to present as polypoid masses or cysts in the vagina or vulva of young to middle-aged women [30, 31]. In contrast to embryonal rhabdomyosarcoma, these tumors are slow growing, devoid of pleomorphic cells and composed almost entirely of well-differentiated strap cells arranged in a myxomatous or collagenous background. A cambium layer is not identified and mitotic activity is scant.

Leiomyosarcoma vs embryonal rhabdomyosarcoma
Rare primary vaginal [32, 33] and cervical [26] leiomyosarcomas have been reported. Myxoid variants of leiomyosarcoma may resemble embryonal rhabdomyosarcoma, and pleomorphic leiomyosarcoma can appear similar to pleomorphic rhabdomyosarcoma. Cervical leiomyosarcoma and rhabdomyosarcoma are both very uncommon tumors, but their histologic appearance frequently overlaps when they are composed predominantly of spindle cells. Embryonal rhabdomyosarcoma, when spindled and growing in fascicles, frequently has a subtle moth-eaten appearance that result from a heterogeneous admixture of cells, some containing densely eosinophilic cytoplasm and others clear or amphophilic cytoplasm; round rhabdomyoblasts with bright red cytoplasm are often haphazardly intermixed. The low power appearance of leiomyosarcoma, in contrast, is generally more uniform. Most embryonal rhabdomyosarcomas with an infiltrative, spindle cell appearance underlie a botryoid tumor and/or are clearly epitheliotropic. Leiomyosarcomas, in contrast, are usually more deeply seated lesions. Skeletal muscle-specific immunostains are useful for distinguishing the two entities, but be aware that diffuse desmin expression is expected in both.

Mullerian adenosarcoma vs embryonal rhabdomyosarcoma
Adenosarcoma and embryonal RMS both share polypoid growth and stromal condensation underneath epithelium, but only botryoid RMS typically contains conspicuous myxoid stroma and the sprinkling of small cellular aggregates of dark blue cells set in a paucicellular background. In contrast to adenosarcoma, RMS does not exhibit phyllodes-like growth or intraglandular stromal papillae.

Carcinosarcoma vs embryonal rhabdomyosarcoma
It is necessary to exclude stromal-predominant carcinosarcomas by searching carefully for lesional epithelium with a malignant appearance. However, it is generally assumed that some genital pleomorphic rhabdomyosarcomas might represent carcinosarcomas in which the epithelial component is overgrown by stroma or is not sampled. Alveolar soft part sarcoma is covered in the discussion of epithelioid smooth muscle tumors, case 4.

A Managerial Approach

A) Polypoid tumors:
Two of the most common entities confused with botryoid embryonal RMS, a highly aggressive tumor in adults, are benign polyps (endocervical and mesodermal stromal polyps) and cervical adenosarcoma. None of these entities typically contains the conspicuous myxoid stroma that is characteristic of botryoid RMS or the sprinkling of small cellular aggregates of dark blue cells set in a paucicellular background. These features can sometimes be appreciated macroscopically, such that gross inspection of a glass slide can suggest the correct diagnosis. Once these features are recognized, it is usually considered mandatory to establish the presence of rhabdomyoblasts, although in some cases, the findings on examination of a picture-perfect H&E slide are sufficient to at least strongly suggest the diagnosis. Either a skeletal muscle-specific immunostain such as myogenin or myo D1 or diagnostic cross striations are considered acceptable for establishing skeletal muscle differentiation. The presence of rhabdomyoblasts excludes a diagnosis of benign endocervical polyp, mesodermal stromal polyp and adenosarcoma lacking heterologous elements.

Benign polyps are treated with polypectomy whereas cervical rhabdomyosarcomas in adults are treated with hysterectomy followed by combination chemotherapy and radiation. In children, whose RMS survivals are superior to those reported for adults, biopsy (not hysterectomy) followed by radiation and, usually, chemotherapy is the standard of care. Adenosarcoma patients whose tumors are organ-confined and lack stromal overgrowth or heterologous elements are generally treated with hysterectomy, but not adjuvant therapy.

The differential diagnosis of a polypoid cervical tumor containing rhabdomyoblasts still includes adenosarcoma and carcinosarcoma (MMMT) with heterologous elements. Of course, every effort should be made to distinguish between these tumors, but the mere presence of malignant rhabdomyoblasts seems to place the patient in a very unfavorable risk category. Patients with stage I uterine carcinosarcomas containing rhabdomyoblasts have survivals that are indistinguishable from patients with pure RMS (see case 3) and there is a recent abstract suggesting that adenosarcomas containing rhabdomyoblasts are similarly aggressive, although this may not apply for small cervical lesions. The distinction between these entities rests predominantly on the examination of multiple sections from a well sampled tumor. In contrast to botryoid RMSs, adenosarcomas contain, at least focally, a phyllodes like appearance, and carcinosarcoma, of course, typically shows foci of high grade carcinoma.

Despite the fact that overall survivals are likely to be similar across these tumor types, therapeutic strategies usually differ. First, radical hysterectomy is sometimes favored if adenosarcoma or carcinosarcoma is recognized to be deeply invasive preoperatively. Carcinosarcoma patients are typically treated with both chemotherapy and radiation therapy, although the chemotherapeutic agents generally differ from those used for RMS. Treatment recommendations for adenosarcomas containing rhabdomyoblasts, however, are poorly defined.

In summary, check for the presence of a polyp with extensive myxoid stroma and small aggregates of immature-appearing stromal cells. If present, confirm rhabdomyoblastic differentiation and search for foci of carcinoma or phyllodes like growth. Liberally section large tumors and hesitate to establish a final diagnosis given small samples. It is not always possible to differentiate RMS versus carcinosarcoma and adenosarcoma containing rhabdomyoblasts when samples are small, distorted and not representative.

B) Invasive spindle cell tumors:
Cervical leiomyosarcoma and RMS are both very uncommon tumors, but their histologic appearance frequently overlaps when they are composed predominantly of spindle cells with obvious nuclear features of malginancy. Embryonal RMS, when spindled and growing in fascicles, frequently has a subtle moth-eaten appearance that results from a heterogeneous admixture of cells, some containing densely eosinophilic cytoplasm and others clear or amphophilic cytoplasm; round rhabdomyoblasts with bright red cytoplasm are often haphazardly intermixed. The low power appearance of leiomyosarcoma, in contrast, is generally more uniform. Most embryonal RMSs with an infiltrative, spindle cell appearance underlie a botryoid tumor and/or are clearly epitheliotropic. Leiomyosarcomas, in contrast, are usually more deeply seated lesions. Skeletal muscle-specific immunostains are useful for distinguishing the two entities.

Leiomyosarcoma patients are generally treated with hysterectomy. Radiation and chemotherapy are usually reserved for patients with tumors with extrauterine spread. Chemotherapy is sometimes also used in an experimental setting for patients with organ-confined leiomyosarcoma.

Very rare examples of spindle cell RMS involving the vulva have been reported. While considered part of the spectrum of embryonal RMS, these tumors do not show the obvious cytologic atypia and immaturity described above in the infiltrative tumors that underlie botryoid RMS. In contrast, these tumors histologically resemble leiomyoma, fibromatosis, myofibromatosis or, perhaps, grade I fibrosarcoma; they do not resemble typical uterine leiomyosarcoma. I therefore recommended myo D1 or myogenin immunostains for all paracervical and vulvar tumors that resemble leiomyoma, fibromatosis, myofibromatosis and grade I fibrosarcoma.

References
  1. Hawkins WG, Hoos A, Antonescu CR, et al. Clinicopathologic analysis of patients with adult rhabdomyosarcoma. Cancer. 2001;91:794-803.

  2. Ferrari A, Dileo P, Casanova M, et al. Rhabdomyosarcoma in adults. A retrospective analysis of 171 patients treated at a single institution. Cancer. 2003;98:571-580.

  3. Little DJ, Ballo MT, Zagars GK, et al. Adult rhabdomyosarcoma: outcome following multimodality treatment. Cancer . 2002;95:377-388.

  4. Folpe AL, McKenney JK, Bridge JA, Weiss SW. Sclerosing rhabdomyosarcoma in adults: report of four cases of a hyalinizing, matrix-rich variant of rhabdomyosarcoma that may be confused with osteosarcoma, chondrosarcoma, or angiosarcoma. Am J Surg Pathol. 2002 Sep;26(9):1175-83. .

  5. Copeland LJ, Sneige N, Stringer CA, Gershenson DM, Saul PB, Kavanagh JJ. Alveolar rhabdomyosarcoma of the female genitalia. Cancer. 1985 Aug 15;56(4):849-55.

  6. Nascimento AF, Fletcher CD. Spindle cell rhabdomyosarcoma in adults. Am J Surg Pathol. 2005 Aug;29(8):1106-13

  7. Andrassy RJ, Wiener ES, Raney RB, et al. Progress in the surgical management of vaginal rhabdomyosarcoma: a 25-year review from the Intergroup Rhabdomyosarcoma Study Group. J Pediatr Surg. 1999;34:731–734.

  8. Crist W, Gehan EA, Ragab AH, et al. The Third Intergroup Rhabdomyosarcoma Study. J Clin Oncol. 1995;13:610–630.

  9. Joshi D, Anderson JR, Paidas C, et al. Age is an independent prognostic factor in rhabdomyosarcoma: a report from the Soft Tissue Sarcoma Committee of the Children's Oncology Group. Pediatr Blood Cancer. 2004;42:64–73.

  10. Martelli H, Oberlin O, Rey A, et al. Conservative treatment for girls with nonmetastatic rhabdomyosarcoma of the genital tract: a report from the Study Committee of the International Society of Pediatric Oncology. J Clin Oncol. 1999;17:2117–2122.

  11. Qualman SJ, Coffin CM, Newton WA, et al. Intergroup Rhabdomyosarcoma Study: update for pathologists. Pediatr Dev Pathol. 1998;1:550–561.

  12. Raney RB, Anderson JR, Barr FG, et al. Rhabdomyosarcoma and undifferentiated sarcoma in the first two decades of life: a selective review of intergroup rhabdomyosarcoma study group experience and rationale for Intergroup Rhabdomyosarcoma Study V. J Pediatr Hematol Oncol. 2001;23:215–220.

  13. Ferguson SE, Gerald W, Barakat RR, et al. Clinicopathologic features of rhabdomyosarcoma of gynecologic origin in adults, in press, Am J Surg Pathol 2007 Mar;31(3): 382-9.

  14. Arndt CA, Donaldson SS, Anderson JR, et al. What constitutes optimal therapy for patients with rhabdomyosarcoma of the female genital tract? Cancer. 2001;91:2454-2468.

  15. Leuschner I, Harms D, Mattke A, Koscielniak E, Treuner J. Rhabdomyosarcoma of the urinary bladder and vagina: a clinicopathologic study with emphasis on recurrent disease: a report from the Kiel Pediatric Tumor Registry and the German CWS Study Am J Surg Pathol. 2001 Jul;25(7):856-64.

  16. Daya DA, Scully RE. Sarcoma botryoides of the uterine cervix in young women: a clinicopathological study of 13 cases. Gynecol Oncol. 1988;29:290-304.

  17. Wang NP, Marx J, McNutt MA. Expression of myogenic regulatory proteins (myogenin and MyoD1) in small blue round cell tumors of childhood. Am J Pathol. 1995 Dec;147(6):1799-810.

  18. Dias P, Parham DM, Shapiro DN, Webber BL, Houghton PJ. Myogenic regulatory protein (MyoD1) expression in childhood solid tumors: diagnostic utility in rhabdomyosarcoma. Am J Pathol. 1990 Dec;137(6):1283-91.

  19. Evaluation of new monoclonal anti- Are myogenin and myoD1 expression specific for rhabdomyosarcoma? A study of 150 cases, with emphasis on spindle cell mimics.Am J Surg Pathol. 2001 Sep;25(9):1150-7.

  20. Cessna MH, Zhou H, Perkins SL, Tripp SR, Layfield L, Daines C, Coffin CM.Are myogenin and myoD1 expression specific for rhabdomyosarcoma? A study of 150 cases, with emphasis on spindle cell mimics.Am J Surg Pathol. 2001 Sep;25(9):1150-7.

  21. Morotti RA, Nicol KK, Parham DM, Teot LA, Moore J, Hayes J, Meyer W, Qualman SJ; Children's Oncology Group. An immunohistochemical algorithm to facilitate diagnosis and subtyping of rhabdomyosarcoma: the Children's Oncology Group experience. Am J Surg Pathol. 2006 Aug;30(8):962-8.

  22. Kaku T, Silverberg SG, Major FJ, Miller A, Fetter B, Brady MF. Adenosarcoma of the uterus: a Gynecologic Oncology Group clinicopathologic study of 31 cases. Int J Gynecol Pathol. 1992;11(2):75-88.

  23. Zaloudek CJ, Norris HJ. Adenofibroma and adenosarcoma of the uterus: a clinicopathologic study of 35 cases. Cancer. 1981 Jul 15;48(2):354-66.

  24. Clement PB. Mullerian adenosarcomas of the uterus with sarcomatous overgrowth. A clinicopathological analysis of 10 cases. Am J Surg Pathol. 1989 Jan;13(1):28-38.

  25. Baker PM, Moch H, Oliva E.Unusual morphologic features of endometrial stromal tumors: a report of 2 cases. Am J Surg Pathol. 2005 Oct;29(10):1394-8.

  26. Fadare O. Uncommon sarcomas of the uterine cervix: a review of selected entities. Diagn Pathol. 2006 Sep 18;1:30.

  27. Nucci MR, Young RH, Fletcher CD. Cellular pseudosarcomatous fibroepithelial stromal polyps of the lower female genital tract: an underrecognized lesion often misdiagnosed as sarcoma. Am J Surg Pathol. 2000 Feb;24(2):231-40.

  28. Tai LH, Tavassoli FA. Endometrial polyps with atypical (bizarre) stromal cells. Am J Surg Pathol. 2002 Apr;26(4):505-9.

  29. Hartmann CA, Sperling M, Stein H. So-called fibroepithelial polyps of the vagina exhibiting an unusual but uniform antigen profile characterized by expression of desmin and steroid hormone receptors but no muscle-specific actin or macrophage markers. Am J Clin Pathol. 1990 May;93(5):604-8.

  30. Chabrel CM, Beilby JO. Vaginal rhabdomyoma. Histopathology. 1980 Nov;4(6):645-51.

  31. Iversen UM. Two cases of benign vaginal rhabdomyoma. Case reports. APMIS. 1996 Jul-Aug;104(7-8):575-8.

  32. Curtin JP, Saigo P, Slucher B, Venkatraman ES, Mychalczak B, Hoskins WJ. Soft-tissue sarcoma of the vagina and vulva: a clinicopathologic study. Obstet Gynecol. 1995 Aug;86(2):269-72.

  33. Peters WA 3rd, Kumar NB, Andersen WA, Morley GW. Primary sarcoma of the adult vagina: a clinicopathologic study. Obstet Gynecol. 1985 May;65(5):699-704.