A Retrospective Study of Adipocytic Tumours Received at a Tertiary Care Center

Introduction: Adipocytic tumours comprise a large proportion of the vast histomorphological spectrum of soft tissue tumours. They range from benign lipomas to malignant liposarcomas with an entire range of various histological sub-types in between. Liposarcomas account for 15-20% cases of soft tissue sarcomas diagnosed. They are characterized with a high recurrence rate, progression to higher grade with time making their correct and prompt diagnosis imperative. Aims: To analyze the clinicopathological profile of adipocytic tumours received at a tertiary care center over a period of three years. To determine the distribution of adipocytic tumours among different age groups and gender. To ascertain the most common site of occurrence/organ involved. To determine the most common histopathological subtypes among the benign and malignant adipocytic tumours. Study Design: Retrospective Descriptive study. Place and Duration of Study: Saveetha Medical College and Hospital, between July 2017-June 2020. Methodology: All cases of adipocytic tumours (218) inclusive of both resection and biopsy specimens received during the study period were included and their case records were accessed. The demographic details were obtained from the case records at the Medical Records Division and the histomorphological findings from the histopathology registers at the Department of Pathology. Original Research Article Agarwal et al.; JPRI, 33(57A): 459-467, 2021; Article no.JPRI.75841 460 Results: In this study, from a total of 20,767 specimens received at our tertiary care center during the period of study, 1.05% (218) were adipocytic tumours, of which 97.25% (212) were benign lipomas and 2.75% (6) were malignant liposarcomas. Out of the total number of malignant tumours (1050) received during the period of study, 2.95% (31) were soft tissue sarcomas, out of which 19.35% (6) cases were liposarcomas. Among the liposarcomas received at our center, 50% (3) cases were well differentiated liposarcoma, 33.3% (2) cases were pleomorphic liposarcoma and 16.7% (1) cases were dedifferentiated liposarcoma.


INTRODUCTION
Soft tissue tumours exhibit vast variations in their histomorphology making them some of the most challenging diagnoses faced by pathologists worldwide. Adipocytic tumours form a large portion of these soft tissue tumours [1]. They range from benign lipomas to malignant liposarcomas with an entire spectrum of various histomorphological sub-types in between [2]. According to the WHO Classification of tumours of Soft tissue and Bone, benign adipocytic lesions include lipoma, lipomatosis, angiolipoma, myolipoma, spindle cell lipoma, and a new entity the atypical spindle cell/pleomorphic lipoma [2]. The lipomas are the most common soft tissue tumour in adults, comprising of at least 30% of all benign soft tissue tumours [2,3]., whereas liposarcomas comprise the more common soft tissue sarcoma (STS) subtypes, accounting for approximately 15% to 20% of all the soft tissue sarcomas [4]. Liposarcomas encompass a histologically diverse group of lesions ranging from locally aggressive well differentiated liposarcoma to highly malignant pleomorphic, myxoid and dedifferentiated liposarcomas, and a new addition-myxoid pleomorphic liposarcoma. Liposarcomas represent a significant proportion of consultation cases and the diagnosis of the histopathological subtype often poses a challenge [5]. Among the liposarcomas, the well differentiated liposarcoma is a locally aggressive tumour, with high rates of local recurrence and a propensity to dedifferentiate [5]. Dedifferentiated liposarcoma is a highly malignant tumour, with very high chances of local recurrence and enormous metastatic potential [5]. Their high chances of recurrence, progression to a higher grade with time, and metastatic potential make an early and correct histopathological diagnosis of liposarcomas imperative.

MATERIALS AND METHODS
This study was conducted at Saveetha Medical College, Chennai, India. It was a retrospective descriptive study wherein hematoxylin and eosinstained slides of sections of formalin fixed paraffin embedded tissue blocks of all cases of adipocytic tumours received at our tertiary care centre over a period of three years (July2017-June2020) were studied. All cases of adipocytic tumours inclusive of both resection and biopsy specimens received during the study period were included. The demographic details and histomorphological findings were obtained from the case records at the Medical Records Department and the Histopathology registers in the Department of Pathology respectively. The tumours were classified according to the WHO classification of tumours of Soft tissue and Bone, 5 th edition, Volume 3, 2020. Statistical analysis was done using descriptive statistics.
The maximum number of adipocytic tumours were found to occur in the age group of 21-50yrs. The lipomas exhibited an almost equal gender distribution. However, liposarcomas showed a slight male preponderance with 4 occurring in men and 2 in women. (Table 1).
In this study, lipomas were found to occur more commonly in the extremities and back. The liposarcomas were most commonly found to be localized in the retroperitoneum. (Table 2) On gross examination of the lipoma specimens, it was observed that most of them presented as well circumscribed, encapsulated, soft tissue tumours except for the intramuscular lipoma

Fig. 1. Gross appearance of lipomas a) Lipoma: Subcuticular tumour with a smooth external surface, covered by thin transparent capsule having a yellowish and greasy cut surface. b)
Intramuscular lipoma: Solid well circumscribed tumour with a yellowish-white cut surface, surrounded by skeletal muscle bundles with noninfiltrating pushing margins. c) Fibrolipoma: Received a skin covered mass with yellowish greasy cut surface which was poorly circumscribed. Their sizes ranged from 0.5 cm to 12.5 cm. The smallest was located in the upper arm and the largest in the anterior abdominal wall. The cut surface of these tumours was yellow or tan white in colour and they were greasy to touch (Fig. 1).
On gross examination of the retroperitoneal liposarcomas all of them had smooth, lobular external surface which was grey white to grey brown in colour and a grey white to greasy yellow appearance of the cut surface with few areas of hemorrhage present.

DISCUSSION
Even though soft tissue tumours are a common entity, our knowledge about these tumours is still limited. Soft tissue pathology is a very dynamic and rapidly evolving field, especially in the current scenario of molecular pathology.  [5,[7][8][9]. However, they are responsible for almost 2% of all deaths attributed to malignancies [3]. As per the inclusion criteria of this study, soft tissue sarcomas constituted 2.95% (31) of all the malignant tumours (1050) reported during the study period, which was almost three times the incidence reported in other studies.
Liposarcomas accounted for 19.35% ( As reported in earlier studies published by Jhonson CN et al and Hui JY, lipomas in this study too showed a slight male preponderance with the incidence of cases peaking in the age group of 31-60yrs [6,7]. They were most commonly located in the upper limbs followed by the back and lower extremities as reported in other studies [6,15]..
The histological variants of benign lipomatous lesions encountered during the course of this study included, 3 cases each of fibrolipoma and angiolipoma, 2 cases of intramuscular lipoma and 1 case of spindle cell lipoma [2]..  [4,14,16].. However, it accounted for only 13.9% cases of liposarcoma in an Asian population [14]..

Studies conducted by
Upon re-examination of H&E-stained sections of liposarcomas we did not come across any case of the new histological subtype of liposarcoma -Myxoid Pleomorphic Liposarcoma [19,20] [5,6,8,16,22]. Some researchers have reported the lower extremities as being the most common site involved followed by retroperitoneum [4,7,23,24].. Liposarcomas were graded using the FNCLCC grading system [2]. The highest FNCLCC grade of 3 was attributed to 1 case of pleomorphic liposarcoma while the other case was of grade 2. All cases of well differentiated liposarcomas were found to be of grade 1. The dedifferentiated liposarcoma was of FNCLCC grade 2 [2,25].

CONCLUSION
Adipocytic tumours comprise a large proportion of the vast histomorphological spectrum of soft tissue tumours. Soft tissue tumours are rare entities and are often ignored by the patients because they most often present as painless masses. This makes it imperative for clinicians to be aware of these entites, to diagnose them early and ensure better management of these cases. Even though several advancements have been made in the field of molecular pathology with respect to liposarcomas, histopathological examination remains the gold standard for proper diagnosis and sub-classification of these tumours. Grading of these tumours helps in further finessing the diagnosis and correlates well with the tumour behaviour impacting prognosis and determining the apt treatment for the case. Most of the liposarcomas are deep seated tumours commonly developing in the retroperitoneal region, making their complete excision a challenge. These tumours if not excised in toto can then progress to a higher grade with greater metastatic potential. Hence, a prompt and accurate diagnosis of these neoplasms is of the utmost importance to ensure better patient management and survival.

CONSENT
It is not applicable.

ETHICAL APPROVAL
The Institutional Review Board approval was obtained and preserved by author(s).