Protocol for the Examination of Specimens From Patients With Tumors of Bone

The College of American Pathologists offers these protocols to assist pathologists in providing clinically useful and relevant information when reporting results of surgical specimen examinations of surgical specimens. The College regards the reporting elements in the “Surgical Pathology Cancer Case Summary (Checklist)” portion of the protocols as essential elements of the pathology report. However, the manner in which these elements are reported is at the discretion of each specific pathologist, taking into account clinician preferences, institutional policies, and individual practice.The College developed these protocols as an educational tool to assist pathologists in the useful reporting of relevant information. It did not issue the protocols for use in litigation, reimbursement, or other contexts. Nevertheless, the College recognizes that the protocols might be used by hospitals, attorneys, payers, and others. Indeed, effective January 1, 2004, the Commission on Cancer of the American College of Surgeons mandated the use of the checklist elements of the protocols as part of its Cancer Program Standards for Approved Cancer Programs. Therefore, it becomes even more important for pathologists to familiarize themselves with these documents. At the same time, the College cautions that use of the protocols other than for their intended educational purpose may involve additional considerations that are beyond the scope of these documents.This protocol applies to malignant bone tumors. Hematopoietic neoplasms are not included. The seventh edition TNM staging system for bone tumors of the American Joint Committee on Cancer (AJCC) and the International Union Against Cancer (UICC) is recommended.Select a Single Response Unless Otherwise Indicated*Data elements with asterisks are not required. However, these elements may be clinically important, but are not yet validated or regularly used in patient management.Specimen (note A)ProcedureTumor Site (select all that apply) (note B)Tumor SizeGreatest dimension: ___ cmHistologic Type (note C)*Mitotic Rate (note D)Necrosis (note D)Histologic Grade (note D)*Lymph-Vascular Invasion (note E)*Additional Pathologic FindingsAncillary StudiesImmunohistochemistryCytogeneticsMolecular PathologyRadiographic Findings (if available) (note F)Select a Single Response Unless Otherwise Indicated*Data elements with asterisks are not required. However, these elements may be clinically important, but are not yet validated or regularly used in patient management.Specimen (note A)Procedure (note G)Tumor Site (select all that apply) (note B)Tumor SizeHistologic Type (notes C and H)*Mitotic Rate (note D)Necrosis (macroscopic or microscopic) (note D)Histologic Grade (note D)Margins (note I)*Lymph-Vascular Invasion (note E)Pathologic Staging (pTNM) (note J)TNM Descriptors (required only if applicable) (select all that apply)Primary Tumor (pT)Regional Lymph Nodes (pN) (note K)Distant Metastasis (pM)*Additional Pathologic FindingsAncillary StudiesImmunohistochemistryCytogeneticsMolecular PathologyRadiographic Findings (if available) (note F)Preresection Treatment (select all that apply)Treatment Effect (select all that apply) (note L)These recommendations are used for all primary malignant tumors of bone except hematopoietic neoplasms, including lymphoma and plasma cell neoplasms.A: Processing.—Tissue specimens from bone tumors optimally are received fresh and unfixed because of the importance of ancillary studies, such as cytogenetics, which require fresh tissue.One section per centimeter of maximum dimension is usually recommended, although fewer sections are needed for very large tumors, especially if they are homogeneous. Tumors known to be high grade from a previous biopsy do not require as many sections as those that were previously diagnosed as low grade because documentation of a high-grade component will change stage and prognosis in the latter case. Sections should be taken of grossly heterogeneous areas, and there is no need to submit more than 1 section of necrotic tumor (always with a transition to viable tumor), with the exception of chemotherapy effect on osteosarcomas and Ewing sarcoma/primitive neuroectodermal tumor (PNET).1 Occasionally, gross pathology can be misleading, and areas that appear to be grossly necrotic may actually be myxoid or edematous. When this happens, additional sections of these areas should be submitted for histologic examination. When estimates of gross necrosis exceed those of histologic necrosis, the greater percentage of necrosis should be recorded on the surgical pathology report. In general, most tumors require 12 sections or fewer, excluding margins. Tumors with greater areas of heterogeneity may need to be sampled more thoroughly.Fresh tissue for special studies should be submitted at the time the specimen is received. Note that classification of many subtypes of sarcoma is not dependent on special studies, such as cytogenetics or molecular genetics, but frozen tissue may be needed for patients to enter into treatment protocols. Discretion should be used in triaging tissue from sarcomas. Adequate tissue should be submitted for conventional light microscopy before tissue has been taken for cytogenetics, electron microscopy, or molecular analysis.It is important to snap freeze a small portion of tissue whenever possible. This tissue can be used for a variety of molecular assays for tumor-specific molecular translocations (see Table) that help in classifying bone tumors.2,3 In addition, treatment protocols increasingly require fresh tissue for correlative studies. Approximately 1 cm3 of fresh tissue (less is acceptable for small specimens, including core biopsies) should be cut into small, 0.2-cm fragments, reserving sufficient tissue for histologic examination. This frozen tissue should ideally be stored at −70°C and can be shipped on dry ice to facilities that perform molecular analysis.B: Location of Neoplasms of Bone.—Radiographic imaging plays an especially critical role in the diagnosis of bone tumors. Close collaboration with an experienced musculoskeletal radiologist and orthopedic surgeon is recommended.The Figure is a diagrammatic representation of the “anatomic” regions of a long bone. These locations are very important in classifying bone tumors. For instance, chondroblastomas almost always arise in the epiphysis. Epiphyses and apophyses are secondary ossification centers and, therefore, are embryonic equivalents. The greater and lesser trochanters are apophyses, whereas the epiphyses are at the ends of long bones.C: Classification of Bone Tumors.—Histologic classification of bone tumors is sufficiently complex that, in many cases, it is unreasonable to expect a precise classification of these tumors based on an intraoperative consultation. A complete understanding of the surgeon's treatment algorithm is recommended before rendering a diagnosis from frozen section. In the case of primary bone tumors, an intraoperative diagnosis of benign versus malignant will generally guide the immediate decision to curette, excise, or wait for permanent sections, and certain therapeutic options may be lost if the wrong path is pursued. Intraoperative consultation is useful in assessing whether lesional tissue is present and whether or not that tissue is necrotic and in constructing a differential diagnosis that can direct the proper triage of tissue for flow cytometry (lymphoma), electron microscopy, and molecular studies and cytogenetics. Tissue triage optimally is performed at the time of frozen section. In many cases, it is important that a portion of tissue be submitted for ancillary studies, even from fine-needle aspiration (FNA) and core needle biopsy specimens, once sufficient tissue has been submitted for histologic evaluation.It is not always possible to classify bone tumors precisely based on biopsy material, especially FNA and core needle biopsy specimens. Whereas pathologists should make every attempt to classify lesions in small biopsy specimens, on occasion, stratification into very basic diagnostic categories, such as lymphoma, carcinoma, melanoma, and sarcoma, is all that is possible. In some cases, precise classification is only possible in open biopsies or resection specimens.Classification of tumors should be made according to the World Health Organization (WHO) classification of bone tumors listed below.4Cartilage TumorsOsteogenic Tumors Chondroblastic Fibroblastic OsteoblasticFibrogenic TumorsFibrohistiocytic TumorsEwing Sarcoma/Primitive Neuroectodermal TumorHematopoietic TumorsGiant Cell TumorsNotochordal TumorsVascular TumorsSmooth Muscle TumorsLipogenic TumorsMiscellaneous TumorsThe grading of bone tumors is largely driven by the histologic diagnosis, and traditionally grading has been based on the Broders system, which assesses cellularity and nuclear features and degree of anaplasia.5 The 7th edition of the AJCC Cancer Staging Manual recommends a 4-grade system.6 G1 and G2 are regarded as low grade and G3 and G4 as high grade. However, we advocate a more pragmatic approach to grading aggressive and malignant primary tumors of bone. Two bone tumors that are locally aggressive and metastasize infrequently, and thus are usually low grade, are low-grade central osteosarcoma and parosteal osteosarcoma. Periosteal osteosarcoma is generally regarded as a grade 2 osteosarcoma. Primary bone tumors that are generally high grade include malignant giant cell tumor, Ewing sarcoma/PNET, angiosarcoma, dedifferentiated chondrosarcoma, conventional osteosarcoma, telangiectatic osteosarcoma, small cell osteosarcoma, secondary osteosarcoma, and high-grade surface osteosarcoma.Grading of conventional chondrosarcoma is based on cellularity, cytologic atypia, and mitotic figures. Grade 1 (low grade) chondrosarcoma is hypocellular and similar histologically to enchondroma. Grade 2 (intermediate grade) chondrosarcoma is more cellular than grade 1 chondrosarcoma, has more cytologic atypia and greater hyperchromasia and nuclear size, or has extensive myxoid stroma. Grade 3 (high grade) chondrosarcoma is hypercellular, pleomorphic, and contains prominent mitotic activity. Mesenchymal chondrosarcoma, fibrosarcoma, leiomyosarcoma, liposarcoma, malignant fibrous histiocytoma (pleomorphic sarcoma, NOS), and other “soft tissue-type” sarcomas that rarely occur in bone can be graded according to the French Federation of Cancer Centers Sarcoma Group (FNCLCC) grading system7 (see the College of American Pathologists' protocol for soft tissue tumors8).Chordomas are locally aggressive lesions with a propensity for metastasis late in their clinical course and are not graded. Adamantinomas tend to have a low-grade clinical course, but that is variable. Fortunately, they are very rare. According to the WHO classification of tumors of bone, adamantinomas are considered low grade.Grade 1 (Low Grade)Grade 2Grade 3 (High Grade)Variable GradeThe 7th edition of the AJCC/UICC staging system for bone tumors includes a 4-grade system but it effectively collapses into high grade and low grade.6,9 Grading in the TNM grading system is based on differentiation only and does not generally apply to sarcomas.For purposes of using the AJCC staging system (see note K), 3-grade systems can be converted to a 2-grade (TNM) system as follows: grade 1, low grade; grade 2 and grade 3, high grade.Lymph-vascular invasion (LVI) indicates whether microscopic lymph-vascular invasion is identified. Lymph-vascular invasion includes lymphatic invasion, vascular invasion, or lymph-vascular invasion. By AJCC/UICC convention, LVI does not affect the T category, indicating the local extent of a tumor, unless specifically included in the definition of a T category.Radiographic imaging plays an especially critical role in the diagnosis of bone tumors. Close collaboration with an experienced musculoskeletal radiologist and orthopedic surgeon is recommended.The following is a list of guidelines to be used in defining what type of procedure has been performed. This is based on the surgeon's intent and not based on the pathologic assessment of the margins.Intralesional Resection: Leaving gross tumor behind. Partial debulking or curettage are examples.Marginal Resection: Removing the tumor and its pseudocapsule with a relatively small amount of adjacent tissue. There is no gross tumor at the margin; however, microscopic tumor may be present. Note that occasionally, a surgeon will perform an excisional biopsy, which effectively accomplishes the same thing as a marginal resection.Segmental/Wide Resection: An intracompartmental resection. A single piece of bone is resected, including the lesion and a cuff of normal bone.Radical Resection: The removal of an entire bone, or the excision of the adjacent muscle groups if the tumor is extracompartmental.Because of extensive treatment effects, such as necrosis, fibrosis, and chemotherapy-induced and radiation-induced pleomorphism, it may not be possible to classify some lesions when either they were never biopsied or the biopsy was insufficient for a precise diagnosis.It has been recommended that for all margins less than 2 cm, the distance of the tumor from the margin be reported in centimeters.10 However, there is a lack of agreement on this issue. We recommend specifying the location of all margins less than 2 cm. Margins from bone tumors should be taken as perpendicular margins, if possible. If the tumor is greater than 2 cm from the margin, the marrow can be scooped out and submitted as a margin.The 7th edition TNM staging system for bone tumors of the AJCC and the UICC is recommended.6,9The classification is to be applied to all primary tumors of bone. Anatomic site is known to influence outcome; therefore, outcome data should be reported specifying site. Site groups for bone sarcoma are the following: extremity, pelvis, and spine. Pathologic staging includes pathologic data obtained from examination of a resected specimen sufficient to evaluate the highest T category; histopathologic type and grade; regional lymph nodes, as appropriate; or distant metastasis. Because regional lymph node involvement from bone tumors is rare, the pathologic stage grouping includes any of the following combinations: pT pG pN pM or pT pG cN cM or cT cN pMFor identification of special cases of TNM or pTNM classifications, the “m” suffix and the “y” and “r” prefixes are used. Although they do not affect the stage grouping, they indicate cases needing separate analysis.The “m” suffix indicates the presence of multiple primary tumors in a single site and is recorded in parentheses: pT(m)NM.The “y” prefix indicates those cases in which classification is performed during or following initial multimodality therapy (ie, neoadjuvant chemotherapy, radiation therapy, or both chemotherapy and radiation therapy). The cTNM or pTNM category is identified by a “y” prefix. The ycTNM or ypTNM categorizes the extent of tumor actually present at the time of that examination. The “y” categorization is not an estimate of tumor before multimodality therapy (ie, before initiation of neoadjuvant therapy).The “r” prefix indicates a recurrent tumor when staged after a documented disease-free interval: rTNM.Because of the rarity of lymph node involvement in sarcomas, the designation NX may not be appropriate and could be considered N0 if no clinical involvement is evident.Residual Tumor (R)Tumor remaining in a patient after therapy with curative intent (eg, surgical resection for cure) is categorized by a system known as R classification, shown below.For the surgeon, the R classification may be useful to indicate the known or assumed status of the completeness of a surgical excision. For the pathologist, the R classification is relevant to the status of the margins of a surgical resection specimen. That is, tumor involving the resection margin on pathologic examination may be assumed to correspond to residual tumor in the patient and may be classified as macroscopic or microscopic according to the findings at the specimen margin(s).Regional lymph node metastasis is extremely rare in adult bone sarcomas. Nodes are not sampled routinely, and it is not necessary to exhaustively search for nodes. When present, regional lymph node metastasis has prognostic importance and should be reported.It is essential to estimate neoadjuvant treatment effect in primary Ewing sarcoma/PNET and osteosarcoma of bone because these have been shown to have prognostic significance.1,11–14 An entire representative slice of the tumor taken through the long axis should be mapped using a grid-pattern diagram, photocopy, or radiologic film to indicate the site for each tumor block. In addition, a section of tumor perpendicular to the long axis should be sampled at the rate of 1 section per centimeter. Areas of soft tissue extension and the interface of tumor with healthy tissue should also be sampled. Prognostically significant therapy response in osteosarcoma, according to most series, is defined at 90%, with those tumors showing 90% therapy response associated with a favorable prognosis.11,12 There are 2 protocols to assess response to therapy in Ewing sarcoma. Response can be assessed in the same manner as osteosarcoma or by the Picci system, which is expressed as grade I (macroscopic viable tumor), grade II (microscopic viable tumor), or grade III (no viable tumor).13,14The authors have no relevant financial interest in the products or companies described in this article.