Uterine leiomyomas with lymphoid infiltration simulating lymphoma. A report of seven cases

Follicular Dendritic Cell Sarcoma of Uterine Corpus: Report of 2 Cases

Follicular dendritic cell sarcoma is a rare dendritic/histiocytic tumor of intermediate malignant potential, which often involves extranodal sites, most commonly the gastrointestinal tract and mediastinum with only 5 cases reported in the female genital tract. We present the clinical and pathologic features of 2 such examples arising in the uterine corpus. Both patients (63 and 72-yr old) presented with postmenopausal bleeding and underwent an endometrial biopsy diagnostic of follicular dendritic cell sarcoma that was followed by hysterectomy. The tumors were polypoid, 3.5 and 5.0 cm, and were confined to the endometrium. Microscopically, ovoid to round to spindled tumor cells with pale eosinophilic cytoplasm and vesicular nuclei were arranged predominantly in sheets with an accompanying lymphocyte-rich inflammatory infiltrate. The tumor cells were positive for CD35, CD23, D2-40 in both tumors and additionally positive for CD21 in 1 tumor, all highlighting cell bodies and processes. Patients were alive without evidence of disease at 1 and 4 years with no adjuvant treatment. These cases highlight the importance of entertaining a broad differential diagnosis in lesions with epithelioid and/or spindled morphology involving the uterus.

Leiomyoma With Massive Lymphoid Infiltration: 2 Cases With Lymphocytic Vasculopathy and Angiocentric Germinal Centers

Uterine leiomyoma with massive lymphoid infiltration is characterized by a dense lymphoid infiltrate and germinal centers sparing the adjacent myometrium. Only few reports describe this entity and its etiology is unknown. This rare lesion may also exhibit lymphocytic vasculopathy but this has only been reported in the setting of GnRH agonist exposure. We report 2 cases of uterine leiomyoma with massive lymphoid infiltration in which only 1 patient was exposed to GnRH agonists. In both cases, histopathologic analysis showed thick-walled vessels with swollen endothelial cells showing evidence of intramural lymphocytic infiltration, red blood cell extravasation, and medial edema. This constellation of findings represented frank vascular damage and lymphocytic vasculopathy. Our findings suggest that lymphocytic vasculopathy in these lesions may be secondary to factors other than GnRH agonists. Furthermore, both cases showed an angiocentric disposition of germinal centers that has scarcely been alluded to in prior reports. This finding may provide a clue in accurately recognizing leiomyoma with massive lymphoid infiltration. Recognition of this lesion will allow one to avoid mistaking it for mimickers such as inflammatory myofibroblastic tumor, lymphoid malignancies, or other inflammatory processes.

Exploring chromosomal abnormalities and genetic changes in uterine smooth muscle tumors

Smooth muscle tumors of the uterus are a diagnostically challenging group of tumors. Molecular surrogate markers reliably distinguishing between benign and malignant tumors are not available. Therefore, the diagnosis is based on morphologic criteria. The aim was to investigate a well-characterized group of challenging uterine smooth muscle tumors consisting of 20 leiomyomas, 13 leiomyomas with bizarre nuclei, and 14 leiomyosarcomas for copy number alterations, MED12 mutations and FH deletions to search for potential diagnostically useful surrogate markers. MED12 mutations were detected in 47, 15, and 25% of leiomyomas, leiomyomas with bizarre nuclei and leiomyosarcomas, respectively. MED12 mutations in leiomyomas with bizarre nuclei were detected outside the hotspot region. FH-deletions were seen in 27, 30.8, and 25% of leiomyomas, leiomyomas with bizarre nuclei and leiomyosarcomas, respectively. By using copy number alteration profiling a clear separation of leiomyomas, leiomyomas with bizarre nuclei and leiomyosarcomas could not be observed. Copy number alterations revealed clear genetic similarities between leiomyomas with bizarre nuclei and leiomyosarcomas. Leiomyosarcomas showed a similar pattern of gains and losses as leiomyomas with bizarre nuclei, with additional copy number alterations and more homozygous losses and high-level amplifications compared to leiomyomas with bizarre nuclei. In conclusion, this study demonstrates that known FH-deletions, a recurrent molecular change in leiomyomas, occur in morphologically challenging variants of leiomyomas, leiomyomas with bizarre nuclei and leiomyosarcomas. Although MED12 mutations are common in leiomyomas, they infrequently occur in leiomyomas with bizarre nuclei and leiomyosarcomas. The genetic similarities between leiomyomas with bizarre nuclei and leiomyosarcomas raise the intriguing possibility that uterine leiomyomas with bizarre nuclei and leiomyosarcomas are closely related and challenge the traditional concept that leiomyoma with bizarre nuclei is a tumor with just marked 'degenerative' cellular changes. These findings support the hypothesis that tumor progression within uterine smooth muscle tumors might occur.

Unusual Morphologic Features of Uterine Leiomyomas Treated with Gonadotropin Releasing Hormone Agonists: Massive Lymphoid Infiltration and Vasculitis

This report describes 2 unusual morphologic features of leiomyomas in patients who had been treated preoperatively with gonadotropinreleasing hormone (GnRH) agonists. In 1 case there was extensive and widespread infiltration of the leiomyoma by numerous small mature lymphocytes, in keeping with a leiomyoma with massive lymphoid infiltration. In the other leiomyoma there were fibrin and foamy histiocytes within the walls of many arterioles, in keeping with a vasculitis. These 2 features, massive lymphoid infiltration and vasculitis, have rarely been described in association with GnRH agonists. Since GnRH agonists are increasingly being used in the management of uterine leiomyomas, pathologists should be aware of these unusual morphologic features in order to avoid diagnostic confusion.

Primary diffuse large B cell lymphoma arising from a leiomyoma of the uterine corpus

Background

Primary diffuse large B cell lymphoma (DLBCL) of the uterus is rare, and primary DLBCL arising from a uterine leiomyoma (collision tumor) has not been reported in the literature.

Case presentation

We describe the clinical, histological, immunohistochemical, and molecular features of primary DLBCL arising from a leiomyoma in the uterine corpus. A 73-year-old female patient had a uterine mass for 23 years. An ultrasound scan revealed marked enlargement of the uterus, measuring 18.2 × 13 × 16.3 cm, with a 17.6 × 10.9 × 11.6 cm hypoechoic mass in the uterine corpus. The tumors consisted of medium- to large-sized cells exhibiting a diffuse pattern of growth with a well-circumscribed leiomyoma. The neoplastic cells strongly expressed CD79α, CD20 and PAX5. Molecular analyses indicated clonal B-cell receptor gene rearrangement.

Conclusions

To the best of our knowledge, no previous cases of primary DLBCL arising from a leiomyoma have been reported. It is necessary to differentiate a diagnosis of primary DLBCL arising from a leiomyoma from that of leiomyoma with florid reactive lymphocytic infiltration (lymphoma-like lesion). Careful analysis of clinical, histological, immunophenotypic, and genetic features is required to establish the correct diagnosis.

A unique case of an indolent myometrial T-cell lymphoproliferative disorder with phenotypic features resembling uterine CD8+ resident memory T cells

OBJECTIVE

Indolent extranodal T-cell lymphoproliferative disorders have recently been described as new entities in the gastrointestinal tract and acral sites displaying clonal T-cell receptor (TCR) rearrangement and nonactivated cytotoxic CD8+ T-cell phenotypes.

METHODS/RESULTS

We report a unique case of an atypical myometrial T-cell lymphoproliferation in a 39-year-old multiparous woman, which shares many of the features mentioned above: CD8+/TIA1+/granzyme B- phenotype, clonal TCR rearrangement and indolent course.

CONCLUSION(S)

We hypothesize that it might derive from a subset of uterine nonrecirculating CD8+ resident memory T cells expanded after repeated exposure to allo-extravillous trophoblastic antigen.

[Uterine leiomyoma with massive lymphoid infiltration: case report]

Uterine leiomyoma with massive lymphoid infiltration is a rare and unusual pathological finding; only 20 cases have been reported in the literature. We report a case of this unusual lesion in a 35-year-old woman who underwent a myomectomy. On gross examination, the tumor was of white color and firm consistency. Histological sections showed interlacing bundles of spindle shaped cells of low density with moderate to severe lymphocytic infiltrate associated to lymphoid follicles and few plasma cells. Immunohistochemically, the diffusely infiltrating lymphoid cells were predominantly of T cell phenotype. The interspersed spindle shaped cells were positive with alpha smooth muscle actin, desmin and h-caldesmon. The cause of this unusual lesion is not clear, but the recognition of its distinct histological features is important to avoid possible confusion with differential diagnosis including malignant lymphoma, inflammatory pseudotumor and pyomyoma.

Miscellaneous Pseudotumors and Mesenchymal Tumors of the Female Genital Tract

Benign and malignant soft tissue tumors and pseudotumors can rarely arise anywhere in the female genital tract. Their pathologic features as well as behavior typically overlap with those described in tumors involving typical locations. However, due to their rarity, not infrequently these tumors represent a diagnostic challenge. Their diagnosis should be based on careful gross examination, thorough sampling, and morphologic evaluation, applying a selected immunohistochemical panel and molecular studies. Accurate classification of these tumors is important because their clinical behavior, prognosis, and therapy differ markedly. This article outlines several mesenchymal lesions reported in the female genital tract, encompassing recent histologic, immunohistochemical, and molecular findings, with special emphasis on problems in the differential diagnosis.

Smooth Muscle Tumors of the Female Genital Tract

Smooth muscle tumors are the most common among mesenchymal tumors in the female genital tract. The vast majority of these neoplasms are clinically benign and easy to diagnose. In contrast, leiomyosarcomas are highly aggressive tumors that may pose considerable diagnostic problems when they display unusual (myxoid or epithelioid) morphology, ambiguous histologic features for malignancy, or an unusual anatomic distribution. Diagnostic criteria for these problematic tumors vary depending on the site and type of histologic differentiation, and are based on a combination of 3 major criteria: (1) moderate to severe cytologic atypia; (2) increased mitotic index; and (3) tumor cell necrosis. Certain benign smooth muscle proliferations may show worrisome histologic features or unusual growth patterns, causing concern for leiomyosarcoma. Furthermore, other tumors, including perivascular epithelioid tumors, may mimic leiomyosarcoma. Careful attention to the clinical and anatomic setting, cytologic and architectural features, and immunohistochemical characteristics are helpful in distinguishing these entities. This article discusses conventional smooth muscle tumors as well as unusual subtypes, with emphasis on the diagnostic criteria and problems in differential diagnosis that arise at each site within the female genital tract.

Uterine leiomyoma with massive lymphoid infiltrate after colon cancer chemotherapy: an immunohistochemical investigation with special reference to lysosome-associated membrane protein expression

Uterine leiomyoma with massive lymphoid infiltration is a rare morphologic phenomenon. We describe the first case of uterine leiomyoma with lymphoid infiltration observed in a patient after chemotherapy for sigmoid cancer. We performed immunohistochemical analysis with a panel of antibodies to several markers. Detection of CD20, CD3, Ki67, CD68 and Epstein-Barr virus nuclear antigen assisted in the differential diagnosis and partial elucidation of the pathogenesis. In addition, we examined the lysosome-associated membrane proteins LAMP-1 and LAMP-2 for the first time in this lesion. Their expression was elevated, indicating enhanced autophagy, an indirect sign of degenerative changes in this benign tumor characterized by massive lymphoid infiltration.

Inflammatory myofibroblastic tumor of the uterus: a clinicopathologic study of 6 cases emphasizing distinction from aggressive mesenchymal tumors

Inflammatory myofibroblastic tumor (IMT) is an indolent spindle cell proliferation that can histologically resemble various malignant mesenchymal neoplasms; however, it generally behaves as a benign or locally recurrent tumor. Most IMTs involve the lung, mesentery, omentum, or retroperitoneum. We report the clinical and pathologic features of six IMTs of the uterus, one of which was included in a previous report, and emphasize the histologic and immunohistochemical features that distinguish IMTs from uterine spindle cell neoplasms that require aggressive treatment. Recently, translocations of the anaplastic lymphoma kinase (ALK) gene and immunohistochemical expression of ALK have been reported in IMTs of various anatomic sites. We compared ALK expression in uterine IMTs with that in uterine mesenchymal neoplasms with which it may be confused. Patients with IMT were between 6 and 46 years of age. None had a history of abdominal surgery; three were multiparous. The IMTs ranged from 1 to 12 cm in maximum dimension. Three grew as polypoid masses that arose in the lower uterine segment, and two of these prolapsed through the cervical os. The three other tumors grew as bulky myometrial masses with focally irregular borders and infiltrated the endometrium, parametrium, or cervical stroma. There were three main microscopic patterns: a hypocellular pattern, a fascicular pattern, and a hyalinized pattern. A lymphoplasmacytic infiltrate was present in all of the tumors, and most had a myxoid background. Mitotic activity ranged from 0 to 2 mitotic figures per 10 high power fields (HPF) except in one tumor that focally had up to 8 mitotic figures per 10 HPF. No nuclear atypia or necrosis was present. Immunohistochemical expression of ALK was present in a cytoplasmic pattern in all IMTs tested. No ALK expression was identified in uterine leiomyoma (n = 7), leiomyosarcoma (n = 6), carcinosarcoma (n = 4), endometrial stromal sarcoma (n = 4), or normal uterine tissues. Follow-up ranging from 1.5 years to 5 years in 4 patients with uterine IMTs revealed no recurrence or metastasis. IMTs should be differentiated from aggressive uterine mesenchymal tumors because they can be treated conservatively and have a more favorable prognosis. ALK expression appears to be of diagnostic value in conjunction with other immunohistochemical stains.

Frequency, Histological, and Immunohistochemical Properties of Massive Inflammatory Lymphocytic Infiltration of Leiomyomas of the Uterus: An Entity Causing Diagnostic Difficulties

Massive lymphocytic infiltration of the leiomyomas of the uterus is rare and causes diagnostic difficulties. The objective of this study is to estimate the frequency, to analyze the clinicopathologic features, to explore the possible pathogenetic factors, and to discuss the differential diagnosis of this entity. We reviewed the pathology reports of 379 patients who underwent surgery for leiomyomas at our institution, from 1999 until 2003, and we identified five cases of leiomyomas with massive lymphocytic infiltration. Thereafter, we reviewed the records of these five patients to identify the clinical, ultrasonographic, and surgical findings they had presented. Leiomyomas with lymphocytic infiltration were characterized by the presence of small lymphocytes, few plasma cells, and occasional germinal lymphocytes such as lymphoblasts confined into the leiomyoma. Immunohistochemistry was positive for desmin and leukocyte common antigen and showed a positive reaction to kappa and lambda light chains that is consistent with the polyclonal nature of an inflammatory infiltration. Gross appearance and ultrasonographic and color Doppler findings were the same as of a typical leiomyoma. Lymphocytic infiltration of leiomyomas is a rare histological entity. Although an inflammatory process seems to be the pathogenetic factor, other mechanisms such as an immunological or autoimmune response, a specific human leukocyte antigen alteration, or a viral infection could also be the cause of this entity. Differential diagnosis must be made from malignant lymphoma, pyomyoma, and inflammatory pseudotumor of the uterus, based on their special histological characteristics.

Uterine leiomyoma with prominent lymphoid infiltrate

We present a case of a 35-year-old woman whose myomectomy specimen revealed a leiomyoma nodule diffusely infiltrated by lymphocytes which were shown to be clonal in nature. Lymphoid infiltration of leiomyomas is a rare occurrence, and this is the first case with molecular analysis.

Uterine adenomyoma with lymphoid infiltration simulating lymphoma

BACKGROUND

Uterine leiomyoma with lymphoid infiltration is a rare disease that simulates malignant lymphoma with only nine cases reported to date. We describe the first case of uterine adenomyoma with lymphoid infiltration simulating lymphoma.

CASE

The specimen resected from a 30-year-old Chinese woman was a well-defined firm nodule measuring 5 x 5.5 x 5.5 cm. The cut surface was similar to that of adenomyoma, which contained dark brown spots and a cyst. Microscopically, the tumor comprised smooth muscle cells intermixed with many lymphocytes. Many lymphoid follicles were present, just locating beside one side of thin-walled blood vessels and protruding into the vessels. Endometrial-type glands and stroma were visible in the tumor.

CONCLUSION

We describe the first case of uterine adenomyoma with lymphoid infiltration simulating lymphoma.

Uterine leiomyoma with massive lymphoid infiltration: Case report and review of the literature

Uterine leiomyoma with massive lymphoid infiltration is a rare and unusual pathological finding. Only 13 cases have been reported in English literature. A case of uterine leiomyoma showing massive lymphoid infiltration in a 45-year-old woman is described. The tumor was relatively soft compared with usual leiomyomas. Microscopically, the tumor showed the typical features of leiomyoma with moderate to severe lymphocytic infiltrate consisting of mature lymphocytes, a few plasma cells and occasional histiocytes. This cellular infiltration was confined to the leiomyoma. Immunohistochemically, the diffusely infiltrated lymphoid cells were stained by antibodies to CD45RO, CD3 and CD8. Germinal centers were stained by antibodies to CD20 and CD79a. Some CD68+ histiocytes were seen. Lymphoid infiltration within the leiomyoma is a peculiar histological morphology, although the cause is not clear. The recognition of its distinct histological features is important to avoid possible confusion with differential diagnoses including malignant lymphoma, inflammatory pseudotumor and pyomyoma.

Cotyledonoid hydropic intravenous leiomyomatosis: a new variant leiomyoma

AIMS

We present the histopathological findings of a series of six cases of a benign uterine smooth muscle tumour with an unusual growth pattern.

METHODS AND RESULTS

All cases have the appearances of the recently described dissecting (cotyledonoid) leiomyoma. In addition, three of these lesions demonstrate the features of intravenous leiomyomatosis with varying degrees of hydropic degeneration.

CONCLUSIONS

This combination of phenotypes has not previously been described within the literature; therefore we propose that these are classified as examples of 'cotyledonoid hydropic intravenous leiomyomatosis', a new variant of unconventional leiomyoma.

Recent advances in the pathology of smooth muscle tumours of the uterus

Smooth muscle tumours of the uterus are common and the majority are benign leiomyomas. However, there are some tumours which exhibit unusual morphological features or growth patterns that cause difficulty in their distinction from malignant neoplasms and those with endometrial stromal differentiation. Such lesions are reviewed in this article with detailed descriptions of their morphology, differential diagnosis and correlation with biological behaviour.

Uterine leiomyomas with Eosinophils: a clinicopathologic study of 3 cases

Although leiomyomas (LMs) of the uterus are common, hematopoietic components within these tumors are not. Lymphoid and other hematopoietic elements have been previously recognized, but eosinophilic infiltrates in LMs have received little attention in the literature. The clinical and pathologic features of 3 cases of uterine LM with eosinophilic infiltration were studied. The patients ranged in age from 35 to 62 years and presented with abdominal and/or pelvic pain and abnormal uterine bleeding. None had peripheral blood eosinophilia or clinical evidence of allergy or parasitic infection. One patient had a benign LM, and the other 2 patients had smooth muscle tumors of uncertain malignant potential. The tumors contained variable numbers of eosinophils and Giemsa stains showed variable numbers of mast cells in addition to the eosinophils. We also performed immunohistochemical and in situ hybridization studies to assess for interleukin-5 (IL-5) and eotaxin in these LMs. There was no consistent association between the presence of eosinophils and either IL-5 or eotaxin in smooth muscle cells, suggesting that mechanisms other than IL-5 or eotaxin production may account for the eosinophilia. Because eosinophils are believed to be involved in wound healing, tissue remodeling, and fibrosis, their presence within LMs may reflect a response to tissue injury produced by the neoplasm rather than intrinsic recruitment by chemotactic factors produced by the smooth muscle cells. Their presence, however, does not appear to have any clinical significance.

Uterine leiomyoma with massive lymphocytic infiltration simulating malignant lymphoma. A case report with immunohistochemical study showing that the infiltrating lymphocytes are cytotoxic T cells

Uterine leiomyoma with massive lymphoid infiltration is very rare and may simulate malignant lymphoma. To the best of our knowledge, this is the first description of such a lesion occurring in an Oriental, and the ninth case in the English literature. A 50-year-old Taiwanese woman had urinary frequency and nocturia because of a uterine myoma. The myomectomy specimen was identified as a well-defined tumor, 6.5-cm in diameter, the cut surface of which was pale, white and whorled. A massive lymphocytic infiltration accompanied by plasma cells and histiocytes was noted in the leiomyoma but not in the surrounding non-neoplastic myometrial fibers. Most infiltrating lymphocytes were positive for CD3 and T cell intracellular antigen-1, a cytotoxic marker. The postoperative course was uneventful, and the urinary symptoms improved within a 6-month follow-up period.

Hyalinized Uterine Mesenchymal Neoplasms with HMB-45-Positive Epithelioid Cells: Epithelioid Leiomyomas or Angiomyolipomas? Report of Four Cases

We present 4 cases of uterine mesenchymal tumors that were located mostly in the myometrium in middle-aged women. Grossly the tumors vaguely resembled conventional leiomyomas. All tumors were extremely hyalinized. The tumor cells were remarkable because of their large size and epithelioid shape. They occurred singly or more often in variously sized clusters with pericellular clear spaces looking like a halo. The extracellular matrix often formed lacunae around the neoplastic cells. The lacunar type of growth was somewhat reminiscent of immature cartilage. In some places the cells lined up in vague cord-like structures. The epithelioid cells often grew within vessel walls and subendothelially, simulating angioinvasion. In 2 cases there were periodic acid-Schiff (PAS)-positive, needle-shaped crystalloids in the cytoplasm of the tumor cells. No atypias and no mitoses were found in any of the 4 tumors. Mucicarmine stain was negative in all cases. Immunohistochemically the tumor cells were negative for cytokeratins, synaptophysin, chromogranin, epithelial membrane antigen (EMA) S-100 protein, and inhibin. They were instead strongly positive for smooth muscle actin, desmin and HMB-45. All patients are disease free after a 1-4-year follow-up. Int J Surg Pathol 8(4):323-328, 2000

The pathology of uterine smooth muscle tumors and mixed endometrial stromal-smooth muscle tumors: a selective review with emphasis on recent advances

This review focuses on the pathology of uterine smooth muscle tumors (SMTs), with a particular emphasis on those studies published in the past 15 years that have expanded our knowledge of these tumors which still present diagnostic challenges for the pathologist. Leiomyoma variants, leiomyosarcoma, SMTs of low or uncertain malignant potential, epithelioid SMTs, SMTs with unusual growth patterns, and mixed endometrial stromal-SMTs are discussed.

Massive lymphocytic infiltration of uterine leiomyomas associated with GnRH agonist treatment

AIMS

To report two unusual cases of massive lymphocytic infiltration of uterine leiomyomas, following GnRH agonist treatment. Previous reports have described a variety of alterations in leiomyoma histology following such therapy.

METHODS AND RESULTS

These cases were studied using haematoxylin and eosin stains, and immunohistochemistry for B and T-cell markers (CD20/CD79a and CD3/UCHL-1) was performed. Leiomyomas were heavily infiltrated predominantly by mature lymphocytes of T-cell phenotype. Associated myocyte degenerative changes were present.

CONCLUSIONS

Massive lymphocytic infiltration of leiomyomas may occur as a result of GnRH agonist treatment, although the mechanism is unclear.

Pathology of uterine fibroids

The pathological appearances of uterine leiomyomas at macroscopic, histological and ultrastructural levels are described and illustrated. Features useful in the differential diagnosis from other uterine spindle cell lesions are included, and an outline is given of the variable features found in different studies of the effects of gonadotrophin hormone releasing hormone analogues on uterine leiomyomas.

Large B-cell lymphoma of the uterine corpus: case report with immunohistochemical and molecular study

Primary lymphoma of the uterine corpus (PLUC) is an extremely rare neoplasm. We report a case of PLUC in a 78-year-old woman with vaginal bleeding without hepatosplenomegaly, adenopathies, or bone marrow infiltration, classified as stage I. A diagnosis of diffuse large B-cell lymphoma was made in endometrial curettage tissue. Immunohistochemical study showed tumoral cells of B-cell nature. Two different polymerase chain reaction (PCR) techniques showed immunoglobulin heavy chain gene rearrangement and we could not demonstrate, with PCR technique, either Epstein-Barr virus or papilloma virus infection. Total hysterectomy with bilateral salpingo-oophorectomy was carried out and adjuvant chemotherapy was given. She was alive and free of disease after a follow-up period of 7 years, and the patient has been in perfect health.

The distribution and possible function of gamma interferon-immunoreactive cells in normal endometrium and myometrium

T-lymphocytes are present in normal endometrium, where they may have a role in the control of glandular maturation. T-cell activity could be related to the local secretion of cytokines such as gamma interferon, which has an anti-proliferative effect on endometrial epithelial cells in vitro. We have examined gamma interferon immunoreactivity and T-cell distribution in 24 normal pre-menopausal uteri. Endometrial appearances were representative of all stages of the menstrual cycle. Most cells in the lymphoid aggregates in the stratum basalis were stained by T-cell and gamma interferon antisera. T-lymphocytes were also scattered in glandular epithelium and throughout the stroma of basal and functional layers; immunoreactivity for gamma interferon was less consistent in these cells. There was no alteration in the intensity or distribution of gamma interferon staining in different phases of the menstrual cycle. Endometrial granulocytes (K-cells) present mainly in the late secretory endometria were not reactive with the gamma interferon antiserum. In addition to endometrial staining, T-cells were distributed in all areas of the myometrium in most uteri, and many myometrial lymphocytes were gamma interferon positive. These results support a role for gamma interferon in endometrial physiology, possibly as an inhibitor of epithelial proliferation.