Fine-Needle Aspiration Cytology of Soft Tissue Sarcoma: Benefits and Limitations

Purpose. Examine the benefits and limitations of fine-needle aspiration cytology (FNA) used as the definitive diagnostic method before treatment. Method. Review of the 25 year experience at a multidisciplinary musculo-skeletal centre where FNA is the primary diagnostic approach to soft tissue sarcoma in the extremities and trunk wall and the experience of various experts in the field. Results. FNA has several benefits compared with coarse needle or open surgical biopsy. The most important are rapid preliminary diagnosis, no need for hospitalization and anaesthesia, negligible complications and fear for tumour cell spread. With the collected experience gained during the years a reliable diagnosis of sarcoma is the rule in general and specific-type diagnoses are possible in many histotypes, especially when the cytologic examination is supplemented with ancillary diagnostics. The most important limitations are inability to hit small deep-seated sarcoma and some diagnostic pitfalls such as the correct diagnosis of spindle cell neoplasms, variants of benign lipomatous tumours and ‘new soft tissue tumour entities’. Discussion. Optimal use of FNA calls for certain requirements such as centralization, experience in soft tissue tumour cytology–histopathology, the FNA technique and close co-operation between the orthopaedic surgeon and cytopathologist.


Introduction
O pen surgical biopsy or coarse needle biopsy are w idely considered to be the diagnostic procedures necessary before the de® nitive treatm ent of a soft tissue sarcom a. F ine-needle asp iration and cytodiagnosis (FN A) has not been universally accepted as a pretreatm ent diagnostic m ethod although num erous reports on the use of F N A in the diagnosis of soft tissue tum ours have been published during the last 20 years. 1± 6 T he subsequent review on the bene® ts and lim itations of FN A as the de® nitive diagnostic m ethod of soft tissue sarcom a before treatment is based on a 25 year experience of FN A of soft tissue tum ours in the extremities and trunk wall from the m ultidisciplinary M usculo-Skeletal T umour C entre at the University H ospital, Lund as well as on cited references.

B ene® ts of FNA
F N A offers several advantages com pared w ith open as well as coarse needle biopsy. FN A of soft tissue tum ours is a harmless out-patient procedure. Severe com plications are non-existent; at m ost there is a tenderness for some days after the needling and a local haem orrhage. Anaesthesia and hospitalization are not necessary. In children, a short general anaesthesia m ay be needed, depending on the clinical presentation of the tumour. W hen the aspirations are perform ed by cytopathologists it is easy to perform a rapid staining of the ® rst sm ear and within 10± 15 m inutes ensure that the m aterial is suf® cient and diagnosable and to suggest a prelim inary diagnosis. Further investigations and/or suggested treatm ent can then be discussed with the patient at the ® rst visit, which is im portant when patients are referred from other hospitals. Properly perform ed FN A is the least tissue-invasive diagnostic procedure and the risk for sarcoma-cell spread is negligible.
Com pared with coarse needle biopsy, which is also an out-patient procedure, a rapid prelim inary report is easier to render as well as the sam pling of tum our m aterial from different parts of large tum ours in order to diagnose tum our heterogeneity, w hich can provide im portant diagnostic inform ation (Fig. 1). The econom ical bene® ts are not only due to reduced costs for hospitalization and the use of an operating room, but the num ber of patient visits is also reduced.
The m ost im portant objections against the use of F N A as the de® nitive diagnosis of soft tissue tum ours in general is the proposed inability for the cytopathologist to give a reliable histotype diagnosis and m alignancy grade. 7,8 The bene® ts and lim itations of FN A in the de® nitive diagnosis of a soft tissue sarcom a m ust, however, be related to the proposed treatment. W hen prim ary surgery is considered, the surgeon m ust have a reliable diagnosis of sarcom a. T he type of surgery perform ed depends m ore on the site and size of the sarcom a and its relation to vessels, nerve bundles and periosteum than on the histogenetic type. T hus with this treatm ent m odality the cytopathologist m ust be able to exclude other malignancies as soft tissue m etastases and prim ary soft tissue m alignant lym phom a and to differentiate between benign soft tissue tum ours/ lesions and sarcoma. O n the other hand, when the treatment option is neoadjuvant therapy followed by surgery, the FN A diagnosis m ust equal that of a biopsy or coarse needle specim en w ith regard to speci® c sarcoma type and m alignancy grade.

P rim ary surgery of soft tissue sarcom a
At present the ® ne-needle asp iration cytology of num erous benign soft tissue tumours/lesions as well as soft tissue sarcom a histotypes have been investigated and diagnostic criteria suggested (Table 1).
One important group of lesions in which the bene® ts of FN A are well docum ented is in the diagnosis of the various pseudosarcom atous soft tissue lesions (nodular fasciitis, proliferative fasciitis and m yositis and pseudom alignant m yositis ossi® cans). The clinical presentation of these lesions is often suspicious for m alignancy; rapid growth, ® rm at palpation and ® xed to underlying structures and biopsy specim ens or excised lesions have been m isinterpreted as sarcom a. The F N A cytology of these lesions has been thoroughly studied. 9± 12 It has also been docum ented that the need for surgical intervention m ost often is unnecessary as the   also been docum ented that the need for surgical intervention m ost often is unnecessary as the m ajority of these tumour-like lesions disappe ar completely or greatly dim inish in size some weeks after the needling. 11,13,14 The cytologic app earance in FN A sm ears of the m ost com m on sarcomasÐ pleom orphic sarcom a of the MF H-type, myxo® brosarcom a (Fig. 2), m yxoid, round cell and pleom orphic liposarcom a (Fig. 3), leiom yosarcom a (Fig. 4) and synovial sarcom aÐ has been described in various series of correlative cyto-logic± histologic studies. 15± 22 Less frequent sarcom as such as clear cell sarcom a, alveolar soft part sarcom a, rhabdom yosarcom a and (extraskeletal) Ew ing' s sarcom a/PN ET (peripheral neuroectoderm al tumour) have also been characterized in F N A m aterial. 23± 28 There is a num ber of sarcom a entities which are insuf® ciently characterized in FN A, am ong them especially m alignant vascular tum ours. It is often possible, however, to give a con® dent sarcom a diagnosis in these cases, the evaluation of m alignancy based on the sm ear pattern, the uniform or pleom orphic cytologically m alignant cell population, num erous m itotic ® gures and fragm ents of necrotic tum our tissue.

Neoadju vant therap y follow ed by surgery
At present, neoadjuvant therapy is considered in the sm all round cell sarcom as such as rhabdom yosarcom a, extraskeletal Ewing' s sarcom a, PNE T, and synovial sarcoma and in selected large, deep-seated high-grade m alignant soft tissue sarcoma of various histotypes.
W hen neoadjuvant therapy (radiotherapy or chem otherapy) is part of the de® nitive treatment, the cytodiagnosis m ust include a con® dent histotype diagnosis and in cases of preoperative radiotherapy of deep-seated sarcom a also a reliable m alignancy grading. Cytologic m alignancy grading of soft tissue sarcom a into low or high grade is possib le and is based on the evaluation of cellular and nuclear pleom orphism and atypia, m itotic activity, especially the presence of atypical m itoses, and necrosis. The histogenetic type of a sarcom a m ight also be im portant in the decision of m alignancy grade, for exam ple, pure m yxoid liposarcom a is m ost often a low-grade tum our while synovial sarcom a is high-grade. According to our experience a reliable m alignancy grading into low or high grade m alignant sarcom a is possib le to perform in about 75% of sarcom as needled. 29 The cytologic features of rhabdom yosarcom a, Ew ing' s sarcoma, PN ET , and synovial sarcom a in F N A sm ears have been studied and diagnostic criteria de® ned. Although these criteria may be the basis of a con® dent type-diagnosis the cytologic exam ination should be supplem ented with various ancillary diagnostic m ethods. In F N A aspirates it is possib le to m ake use of the same supplementary techniques as in surgical specim ens and the use of adjunctive diagnostic m ethods in FN A is well docum ented. 25,30± 34 At present routine cytologic exam ination combined with ancillary diagnostics successfu lly and reliably can diagnose m ost sm all round cell sarcom as and synovial sarcom as before the neoadjuvant therapy. In m any pleom orphic high-grade sarcom as it is also possible to de® ne the histotype.

Lim itations of FNA
T he lim itations of FN A in the diagnosis of soft tissue sarcom a are threefold: (a) the sarcom a is not hit with the needle and a false diagnosis m ay be rendered on the reactive cellular changes in the aspirated surrounding tissues; (b) insuf® cient m aterial (poor yield or technically inferior sm ears) from the tum our is evaluated; and (c) m isinterpretation of the aspirated cells. According to our 25 year experience one im portant reason for a false diagnosis is that the m aterial exam ined does not originate from the sarcoma but from the surrounding tissues. In these cases either a benign diagnosis is given or a false sarcom a-type diagnosis is suggested, based on reactive, pseudom alignant cellular changes, especially reactive changes in adipose tissue resem bling liposarcom a or reactive pleom orphic ® broblasts and m yo® broblasts falsely interpreted as originating from a m alignant ® brous histiocytoma. T his is m ost often the case with small deep-seated, inter-or intram uscular sarcom as.
The m ain reason for a false diagnosis is, however, m isinterpretation of the cellular m aterial. T here is a num ber of w ell-docum ented diagnostic dif® culties. O ne of the m ost com m on is the correct evaluation of tumours predom inantly com posed of spindle cells 2,35,36 (Figs 5 and 6). Another im portant pitfall is false m alignant diagnosis of benign lipoma variants as pleom orphic and spindle cell lipom a, hibernom a and lipoblastom a. 17 A rare diagnostic dif® culty is the m isinterpretation of aspirates from soft tissue m etastases from pleom orphic carcinom a

D iscussion
T he clinical bene® ts of FN A in the prim ary, de® nitive diagnosis of soft tissue sarcom a are advantageous, but to reach a reasonably high diagnostic accuracy certain requirem ents should be observed. A close co-operation between the surgeon and cytopathologist is m andatory. The surgeon often w ill decide the insertion point of the needle and when demanding a prelim inary report, discuss the diagnosis w ith the cytopathologist in relation to the clinical history, palpatory ® ndings and radiograph ic investigations, if any. T he ® nal diagnosis should be the com bined evaluation of clinical and radiograph ic data and the cytodiagnosis. In order to avoid false diagnoses due to a faulty asp iration technique and inability to hit the tumour at needling the cytopathologist m ust be a trained aspirator with a fair knowledge of the clinical behaviour and histopathology of soft tissue tum ours. Ultrasound-guided aspirations of sm all deep-seated sarcom a are recom m ended to ensure that the needle is within the tum our.
As soft tissue sarcom as are relatively rare tum ours (in Sw eden the annual incidence is 2± 3/10 6 inhabitants) and m any benign soft tissue tum ours clinically are suspected to be sarcom as, the optim al use of FN A is reached when patients w ith suspected sarcom a are referred with virgin tum ours to m ultidisciplinary m usculo-skeletal centres. Benign soft tissue tumours/lesions are far m ore com m on than soft tissue sarcom as, in order to ensure that the FN A of the majority of sarcom as are perform ed at   (Table 2). O ne challenge for the cytopathologist is the typediagnosis of high-grade deep-seated sarcoma that are candidates for preoperative radiotherapy. W hen the therapy is successful it m ight be dif® cult to diagnose reliably the histogenetic type on the surgical sam ple. Im m unocytochemistry m ay be helpful in suggesting sm ooth muscle or Schwann cell differentiation, but desm in positivity m ay be patchy in pleom orphic leiom yosarcom a and m any m alignant peripheral nerve sheet tumours do not react with the anti S-100 protein antibody. Im m unocytochem istry is, however, of help in the differential diagnosis of soft tissue carcinom a m etastases and soft tissue anaplastic large cell lym phom a versus pleom orphic sarcom a. Electron m icroscopic exam ination of aspirated m aterial is a valuable diagnostic adjunct in pleom orphic leiomyosarcom a and to certify a diagnosis of round cell or pleom orphic liposarcom a. T he diagnosis of monophasic synovial sarcom a is a wellknown problem in FN A cytodiagnosis, but we have had the decisive help of electron m icroscopic studies in a num ber of cases. 22 D N A-ploidy analysis is a lim ited but valuable adjunct. An unequivocal non-diploid cell population is com patible w ith m alignancy and according to our experience high-grade sarcom a. 31 The sm all round cell sarcom as are safe ly diagnosed by the com bined evaluation of the cytologic features and ancillary diagnostics. W ith the aid of im m unocytochem ical staining and ultrastructural investigations rhabdom yosarcom a, extraskeletal Ewing' s sarcom a and PN ET are con® dently diagnosed. D esm in, C D 99 (M IC 2 -antigen), neuron-speci® c enolase and chrom ogranin are valuable antibodies in the type-diagnosis of these tum ours. Cytogenetic and molecular genetic analyses have emerged as powerful diagnostic tools in those sarcom a where diagnostic translocations have been described and the genes involved identi® ed. T he use of cytogenetics in the diagnosis is docum ented in Ewing' s sarcoma and synovial sarcom a 32,33 and it should be possible to m ake use of the know n molecular genetic aberrations in the diagnosis of liposarcom as with a com ponent of myxoid liposarcom a and alveolar rhabdom yosarcom a. W e have recently used RT-PCR for the diagnosis of the PCR for the diagnosis of the SSX1/SYT fusion genes in a case of suspected synovial sarcom a.
The bene® ts of FN A in the de® nitive diagnosis of soft tissue sarcom a outweigh the lim itations when (i) there is a close co-operation between cytopathologist and surgeon (referral of patients to m ultidisciplinary centres), (ii) the diagnosis is based on reliable and reproducible criteria, (iii) ancillary m ethods are part of the diagnosis and (iv) the diagnostic pitfalls are identi® ed.