Case of the Month

Answer:

C. Low grade endometrial stromal sarcoma and endometrial adenocarcinoma, endometroid type

The cervix and lower uterine segment is involved by endometrial adenocarcinoma, endometroid type, FIGO grade 1, from 6-12 o’clock without stromal involvement of the cervix.
There is a separate 5.7 cm posterior uterine mass which is diagnosed as Low Grade Endometrial Stromal Sarcoma.

Discussion:

On initial imaging and gross examination, this tumor was thought to be a leiomyoma due to its well circumscribed nature, whorled cut surfaces, and the high prevalence with which leiomyomata are present  in the uterus. There was no hemorrhage or necrosis, which made leiomyosarcoma not of concern grossly. The histology was not that of a conventional leiomyoma, so the differential was broadened to include a leiomyoma, leiomyosarcoma, endometrial stromal nodule, low grade endometrial stromal sarcoma, high grade endometrial stromal sarcoma, and undifferentiated uterine sarcoma.

In additional to the overall histologic appearance of the tumor resembling that of endometrial stroma, the differential diagnosis was focused toward the endometrial stromal category with immunohistochemical stains which were SMA, Desmin, and Caldesmon negative, effectively ruling out smooth muscle entities such as a leiomyoma or leiomyosarcoma. CD10 and WT-1 were positive, supporting the diagnosis of an endometrial stromal neoplasm.

Microscopically, the tumor showed an exophytic portion composed of densely cellular sheets of uniform small cells with scant cytoplasm and round to oval nuclei. Although the tumor had appeared well circumscribed grossly, microscopic images showed finger like projections or “tongues” of tumor cells invading into the myometrium.  Less than three small finger-like projections like these measuring less than 3 mm in greatest dimension can be seen in an endometrial stromal nodule; however, greater numbers or dimension of such projections  (as seen in this case) exclude this diagnosis. Lymph vascular invasion, as was seen in the case, also excludes the diagnosis for an endometrial stromal nodule. A more malignant entity was thus considered including a low or high grade endometrial stromal sarcoma.

Morphologically, high-grade stromal tumors have a more destructive appearance then low-grade tumors often invading into the outer portion of the myometrium. There are also areas of the low-grade spindled counterpart intermixed with areas that have high-grade round cell morphology. High-grade stromal sarcomas also show more mitotic activity than the low-grade counterpart, typically more than 10 per high-power field. The mitotic activity was low in this case (proliferation index using Ki-76 was <5%), making a high-grade stromal sarcoma less likely. Undifferentiated sarcomas show marked cytologic atypia, brisk mitotic activity, and can even have rhabdoid morphology or a myxoid background.  Due to the infiltrating tumor projections, uniform spindled appearance, staining pattern, and low mitotic activity, the tumor best fits a low grade endometrial stromal sarcoma.

References

1. Kurman RJ, Carcangiu ML, Herrington CS, Young RH. WHO Classification of Tumours of Female Reproductive Organs. Herdon, VA: Stylus Publishing, LLC, 2014. Print pages 135-145.
2. Robboy SJ, et al. Robboy’s Pathology of the Female Reproductive Tract, second edition. China: Churchill, Livingston, Elsevier, 2009. Print pages 427-436.