تازه های پاتولوژی در تومورهای استخوان دی ماه 1395

در واقع باید گفت که شاید تنها جایی در علم که حرف تازه ای برای گفتن وجود ندارد؛ مبحث تومورهای استخوان است.

مهمترین روش تشخیص در تومورهای استخوان همانند صد سال گذشته؛ همان روش معمول در پاتولوژی، یعنی مشاهده بافت به صورت ماکروسکوپی و میکروسکوپی با رنگ آمیزی معمول هماتوکسیلین ائوزین است.

در مورد مهمترین تومور استخوان یعنی استئوسارکوم حتی رنگ آمیزی ایمونوهیستوشیمی هم انجام نمی گیرد و تشخیص تنها با مشاهده بافت به صورت ماکروسکوپی و میکروسکوپی انجام می گیرد.

تنها در تومور یوئینگ است که از روش های تشخیصی جدید تا اندازه ای استفاده می شود (ایمونوهیستوشیمی و FISH)، ولی باز هم در این تومور مشاهده میکروسکوپیک با روش قدیمی حرف اول را می زند.

شاید تنها نکته نه چندان تازه در مورد این تومورها؛ بررسی هیستولوژیک تومور پس از شیمی درمانی باشد.

برای گزارش این تغییرات، روشهای مختلفی وجود دارد.

Essentially, 2 different methods of histologic assessment have been established.

The first, described by Huvos, is based on his method for evaluating osteogenic sarcoma samples.  

In a semiquantitative manner, histologic evaluation is performed by grading the extent of necrosis relative to the percentage of residual viable tumor.

The Huvos system includes 4 grades: Grade 1: little or no evidence of necrosis; Grade 2: necrosis of 50%–90%; Grade 3: necrosis between 90%– 99%; finally, Grade 4: 100% necrosis

This method of histologic grading has been shown to be very effective in the management of Ewing’s sarcoma also.

The extent of necrosis has been directly correlated with improved survival.

However, quantitative measurements are open to criticism. Ewing’s sarcoma differs from osteogenic sarcoma in that it does not produce any major extracellular matrix component, so there is no indicative evidence left by the tumor cells.

Furthermore, in response to chemotherapy, Ewing’s sarcoma cells may disappear completely. For these reasons, there may be a dramatic decrease in tumor volume after preoperative chemotherapy without histologic delineation of where the tumor was located originally.

Because of this potentially large change in tumor volume following neoadjuvant chemotherapy, estimates of tumor necrosis are difficult to calculate based only on the viable cells per unit area of residual tumor.

Consequently, a strictly quantitative method to estimate tumor necrosis may not be appropriate in Ewing’s sarcoma.

However, because pathologists are accustomed to using the well-established Huvos system for osteogenic sarcoma, they are able to apply it accurately to Ewing’s sarcoma.

Instead of estimating the amount of nonviable tumor, Picci et al Instead of estimating the amount of nonviable tumor, Picci et al. proposed evaluating the amount of remaining viable tumor. They developed a method that requires calculating the absolute quantity of viable tumor cells after preoperative chemotherapy, which does not vary with volume changes of the primary tumor.

The scoring system proposed by Picci et al. includes 3 grades.

Grade 1 response represents a tumor with at least 1 macroscopic residual nodule of viable tumor. Individual macroscopic nodules are defined as those that are larger than one 10x magnification field, or as scattered microscopic nodules that individually are smaller than one 10x magnification field but that collectively are larger than one 10x magnification field.

Grade 2 response represents a tumor with only isolated microscopic foci of viable tumor smaller than the size of a 10x magnification field.

Grade 3 response indicates no evidence of viable tumor cells.

This method is easy to interpret because it does not require the calculation of percentages, but it does require an exhaustive examination of the tissue and preparation of multiple section.

Furthermore, this method fails to account for the original tumor size Furthermore, this method fails to account for the original tumor size. For example, the persistence of 1 nodule is graded the same, regardless of whether the tumor volume was 10 cm3 or 200 cm3.

نکته مهم در بررسی نمونه پس از شیمی درمانی نقشه برداری و پاس داده تمام نمونه است.

نقشه برداری نمونه

Akermån stressed that the regional mapping protocol was more important than the type of grading system used. Picci et al. support this point by showing the significance of this regional mapping of the tumor.

They found that viable tumor was more often detected in some of the preferential or sanctuary sites than in the central part of the tumor.

These preferential sites were: (1) in the subperiosteal region of new bone formation, (2) in the soft tissue mass, and (3) in areas of hemorrhage, present in 41% of patients. Furthermore, disease was present in the intramedullary canal in 36% of patients.

Ewing Sarcoma

The biopsy shows extensive new bone formation with an accompanying population of osteoblasts and stromal cells with atypical features but in the absence of mitotic figures.

Another field shows somewhat irregular sclerotic bone, which caused some concern about osteosarcoma yet in absence of anaplastic cells.

Nodule in the adjacent soft tissues is composed of uniform hyperchromatic malignant round cells.

Another focus consists of malignant round cells infiltrating skeletal muscle.

The tumor cells are immunoreactive for vimentin, cytokeratin, and CD99.

An EWS breakapart was demonstrated by FISH studies.

The periodic acid-Schiff stain shows diffuse cytoplasmic positivity.

The tumor cells demonstrate a diffuse cytoplasmic pattern of vimentin positivity by immunohistochemistry.

CD99 or MIC2 immunopositivity shows a diffuse membrane-cytoplasmic pattern with mosaic-like features.

Ewing sarcoma—primitive neuroectodermal tumor is characterized by its most common signature translocation, t(11;22) (q24;q12).

This translocation of the EWS gene is demonstrated by fluorescent in situ hybridization by the presence of a split signal as shown in this study.

Approximately 90% of tumors have an EWS breakapart and the remaining 10% of cases have variant translocations not involving the EWS gene as a fusion partner.

The gross examination of the resected tumor occurs after preoperative chemotherapy in virtually all cases since primary resections are a treatment of the past.

It is to be expected that the gross features are variable from a solid medullary focus of tumor to a hemorrhagic mass extending through the cortex into the subperiosteum of the diaphysis or beyond into the soft tissues.

In some cases, the tumor may involve the medullary cavity along its length with associated cortical thickening.

Though a substantial soft tissue component may have been present before chemotherapy, it is often reduced to a residual subcortical mass or no evidence at all of a mass.

The presence of residual viable tumor should be assessed in a fashion similar to OS. Blocks are obtained from grossly visible tumor and surrounding bone so as to provide a semi- quantitative percentage of tumor death with an optimal index of necrotic tumor in the range of 90% or greater.

Effectiveness of chemotherapy can be judged by imaging studies in particular the soft tissue component.

Fibrosis, hemorrhage, and cyst formation may be the only residual findings in the resected specimen. The prognostic determinants of outcome are location (axial, poor), size (8 cm or greater, poor), and complete surgical resection after chemotherapy, favorable).

The pathologic diagnosis of EWS-PNET is facilitated to a considerable degree with the availability of immunohistochemistry and molecular diagnostics since the basic morphology may be distorted by artifacts created at the time of biopsy and subsequent processing for microscopic examination.

Because these tumors may be extensively hemorrhagic and necrotic, the biopsy itself may be paucicellular.

Otherwise, there are essentially no histopathologic differences between the osseous and extraosseous EWS-PNET.

A monolayer of nonoverlapping polygonal cells have a distinct cell membrane, a uniform round to oval nucleus with finely dispersed chromatin and a small nucleolus, and clear to finely vacuolated cytoplasm in the well-preserved and prepared biopsy.

Mitotic figures are generally inconspicuous, but not in all cases. Indistinct cell borders, overlapping cells, nuclear hyperchromatism, scattered mitotic figures and lobular-trabecular, or rosette-like profiles are other features.

Any degree of anaplasia and substantial pleomorphism should be viewed with a question about the possibility of small cell OS, large cell lymphoma including anaplastic large cell lymphoma, or metastatic alveolar rhabdomyosarcoma.

Foci of necrosis with or without a perithelial arrangement of tumor cells and hemorrhage with a pseudovascular or peliosis-like appearance are other common microscopic features.

Small contracted pyknotic or secondary cells may be seen among the better preserved tumor cells. Whether an artifact or otherwise, the tumor cells may have more spindled features.

If the biopsy has been obtained from the soft tissue component, fibrous stroma with reactive features is often present and some of these nonneoplastic changes can obscure some of the diagnostic findings.