Soft Tissue Tumours: the Surgical Pathologist's Perspective

08_DeSchepper_Soft_Tissue 15.09.2005 13:22 Uhr Seite 107 Chapter Soft Tissue Tumours: the Surgical Pathologist’s 8 Perspective Roberto Salgado, Eric Van Marck Contents Recently, using transcriptional gene profiling comple- mented with, e.g. tissue microarrays, new potential ther- 8.1 Introduction . 107 apeutic markers of histiotype-specific soft tissue tu- 8.2 When Pathology Meets Radiology . 107 mours have emerged, e.g. CD117 (c-kit) and DOG1 for 8.3 When Pathology Meets the Clinics . 108 gastrointestinal stromal tumours, PDGFRb in dermatofi- 8.4 When Morphology is not Enough . 109 brosarcoma protuberans and EGFR1 for synovial sarco- mas, which in some cases might even be able to predict 8.5 World Health Classification of Soft Tissue Tumours 2002 . 111 therapy response and prognosis [1–3]. These advances have led to an increased appreciation of the importance 8.6 To Grade or not to Grade? . 112 that histological typing might have in predicting natural 8.7 Reporting Soft Tissue Tumours . 114 history and treatment sensitivity of soft tissue tumours. 8.8 Gene Expression Profiling Tumour tissue procurement and exact tissue han- and Tissue Microarrays in Soft Tissue Tumours . 114 dling are critical issues to provide the pathologist with 8.9 Conclusions and Future Perspectives . 115 adequate and well preserved tissue, in order to perform References . 115 the necessary ancillary studies for making an exact diagnosis. Cross-talk between pathologists, radiologists and clinicians is crucial in obtaining this goal. 8.2 When Pathology Meets Radiology 8.1 Introduction The importance for the pathologist of both clinical and The diagnosis of soft tissue tumours has always been radiological information cannot be overemphasised. difficult and controversial. This was mainly due to the Some tumours merely occur in children, e.g. rhab- rarity of these lesions, comprising <1% of all malignant domyosarcomas, while others are rare in children and tumours. Nevertheless, according to the Surveillance, are mostly found in adults, e.g. pleiomorphic liposarco- Epidemiology, and End Results (SEER) database, about ma [4]. 15,000 cases of both bone and soft tissue tumours are Magnetic Resonance Imaging (MRI) and Computed diagnosed annually in the US. This puts soft tissue and Tomography (CT) give the pathologist information bone tumours in the same order of magnitude as about the size, consistency, homogeneity, location, pres- myeloma, gliomas and cervical carcinoma. ence or absence of necrosis, infiltration pattern, inter- Previously, the clinical importance of the exact histo- face with adjacent structures, etc. logical typing of soft tissue tumours by the pathologist Anatomic pathologists rendering a diagnosis on was limited, knowing that grade and stage, and not his- mostly limited material without having the advantages tological type determined treatment options. The of clinical and radiological information might be in a pathologist merely served to grade the lesion and to ex- disadvantageous position in many cases. It is imperative clude malignant non-sarcomatous, benign or pseudotu- that pathologists with a special interest in soft tissue tu- moral lesions. The small number of lesions – in particu- mours do at least have a rudimentary knowledge of the lar of single histological types – and the poorly defined radiological and clinical features of the tumours, in pathological criteria are the major sources of discor- analogy with pathologists interested in bone tumours. dances in diagnostic soft tissue pathology. Even in spe- On the other hand, it is equally important to have a ra- cialist centres about 5–10% of soft tissue lesions remain diologist and clinicians with a keen interest in soft tis- unclassified. sue tumour pathology. 08_DeSchepper_Soft_Tissue 15.09.2005 13:22 Uhr Seite 108 108 Roberto Salgado, Eric Van Marck Some soft tissue tumours such as liposarcomas are sion biopsies should only be performed on superficial quite heterogeneous. Therefore, the pathologist might or subcutaneous tumours which are usually smaller aid in choosing which area of the tumour is best suited than 2–3 cm in size. Excision biopsies of larger and/or for sampling, considering that sampling in areas of deep seated masses are best avoided. overt necrosis is best avoided. Sampling near necrotic Open, incisional biopsies are performed in most cen- areas, however, can be meaningful since the presence or tres. Open biopsies enable the pathologist to have absence of necrosis is considered an integral part of enough tissue, not only with a preserved architecture of grading schemes [5]. Meanwhile, in analogy with bone the tumour which is crucial for histological subtyping, tumours, e.g. osteosarcoma and chondrosarcoma, but also for performing ancillary studies, e.g. immuno- imaging features might provide the pathologist with histochemistry, cytogenetic and gene expression profil- spatial features of soft tissue lesions that are highly sug- ing-studies, when deemed necessary. gestive of being the high grade areas of the tumour. For Recently, more emphasis is being placed on the abili- example, chondrosarcomatous tumours having myxoid ty of pathologists to make a reliable diagnosis on rela- areas juxtaposed to cartilaginous areas are highly sug- tively smaller amounts of tissues. This is mainly due to gestive of being of high grade malignancy [6]. Sampling economic reasoning and patient comfort. Core Needle in these areas might be necessary for arriving at an ex- Biopsies (CNB) and Fine Needle Aspiration Biopsies act diagnosis, meanwhile trying to avoid underestima- (FNAB) are temporarily quite popular [7, 8]. The main tion of the malignant potential of the tumour when advantages of both these methods include the feasibili- sampling of non-high grade areas occurs. Sampling is ty in performing these kinds of biopsies in outpatient also imperative for performing additional studies such clinical settings, the minimal risk of complications, the as cytogenetic analysis, as will be explained later. cost-effectiveness and the acceptability of the patient. Estimating the percentage of necrosis preoperatively Moreover, the reduced risk of spilling tumour cells dur- by the radiologist might also be important, since some ing the biopsy procedure and the lack of compromising tumours,e.g.Ewing’s sarcoma and extra-renal rhabdoid the subsequent surgical management are considered tumours, are treated preoperatively, and the pathologist additional features in favour of FNAC or CNB vs open is asked to estimate the percentage of viable tumour tis- biopsy.Spilling of tumour cells and compromising here- sue left after treatment, as a measure of tumour re- with the surgical bed and subsequent therapeutic mea- sponse. This is quite elaborate and subjective since it is sures are often the case when open, incisional biopsies quite impossible, histologically, to distinguish between are performed by inexperienced surgeons. This urges spontaneous or therapy-induced necrosis. that for soft tissue lesions suspicious of being malig- Close collaboration between radiologists and pathol- nant, biopsy procedures should be decided on after in- ogists is important, not only to decide where to sample tense cross-talk between pathologists, radiologists and but also in determining how to sample. clinicians, and should preferable be performed in refer- ence centres. Nevertheless, despite the above-mentioned obvious 8.3 When Pathology Meets the Clinics advantages of sampling limited material, this does not imply that pathologists are willing or able to make a Once the lesion is localised, obtaining a biopsy in the specific diagnosis on small amounts of material. Limit- appropriate tumour area is the next logical step. Ideally, ed sampling might make grading and exact subtyping the biopsy should occur in the centre where the patient quite difficult. Moreover, preoperative chemo- and/or will be treated. It is not surprising that a pathologist of- radiotherapy for some tumours, e.g. Ewing sarcoma, ten requests larger tumour samples or asks for a second might make adequate and reliable histological typing opinion when being confronted with a soft tissue tu- and grading evaluation of resected specimens extreme- mour. This is mainly due to the rarity of the lesions, the ly difficult, if not impossible. lack of adequately defined diagnostic criteria and the Preoperatively, with limited material, especially after “unearthing” of new entities. There are some 50 differ- FNAC, the pathologist is in some cases only able to pro- ent subtypes of soft tissue tumours. Considering the vide diagnoses such as “malignant soft tissue tumour, rarity of the lesions and the difficulties associated in ob- not otherwise specified” or “spindle” or “round cell” tu- taining an adequate biopsy from representative tumour mour.This would imply in some cases that it would even areas, which can only occur once the tumour has been not be possible to know exactly which tumour was investigated thoroughly by adequate imaging means treated, since preoperative therapy might distort mor- (MRI and CT), biopsy procedures in the primary care phology considerably. settings should be discouraged. Biopsy procedures Deep seated lesions, however, are amenable for CNB, without having adequate radiological information giv- avoiding the discomfort of open, incisional biopsy in en by CT or preferable by MRI, should be avoided, un- these specific circumstances. FNAC is indicated mostly less the lesion is small and superficially located. Exci- for assessing local recurrence or metastasis

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