A comparison of the prognoses for deep and subcutaneous sarcomas of the extremities

We evaluated 172 patients who had a soft-tissue sarcoma of the extremity in order to determine whether the prognosis for a subcutaneous sarcoma was better than that for a deep sarcoma. At a median of thirty-six months after the biopsy or definitive operation at our hospital, six of the fifty-two patients who had had a subcutaneous sarcoma had died and one had had a local recurrence; in contrast, forty of the 120 patients who had had a deep sarcoma had died and eight had had a local recurrence. Twenty-five (48 percent) of the subcutaneous sarcomas were malignant fibrous histiocytomas, and thirty-eight (73 percent) were small (five centimeters or less in the largest dimension). The three-year estimates of disease-free survival were 85 percent for the patients who had a subcutaneous sarcoma and 54 per cent for those who had a deep sarcoma (p = 0.002). Although the survival estimates remained significantly different when the groups were matched for histological diagnosis and for intracompartmental location (p = 0.0001 and 0.0006, respectively), they were not significantly different when the groups were matched for the size of the tumor (p = 0.42). A Cox proportional-hazards model confirmed that a tumor size of more than five centimeters and the histological grade are the most significant prognostic factors (p = 0.0007 and p = 0.004, respectively): a tumor size of more than five centimeters was associated with a relative risk of 3.5 (95 per cent confidence interval, 1.7 to 7.3), and a higher histological grade was associated with a relative risk of 4.0 (95 per cent confidence interval, 1.6 to 10.3). Subcutaneous location, when considered separately, was not a significant prognostic factor (p = 0.45). The data indicate that a tumor size of more than five centimeters is a more important prognostic indicator than histological diagnosis, depth, or intracompartmental location.

High-titer immune responses elicited by recombinant vaccinia virus priming and particle boosting are ineffective in preventing virulent SIV infection

Eighteen rhesus monkeys were vaccinated with recombinant vaccinia viruses expressing SIVmac antigens in 3 separate rounds of experiments. Twelve of the monkeys were primed with a trivalent vaccinia virus recombinant expressing Gag, Pol, and Env polypeptides that can assemble into SIV pseudovirion particles and boosted with SIV particles in adjuvant. Four of the monkeys were primed with different vaccinia virus recombinants expressing env or gag+env followed by SIV particle boosts; two received vaccinia virus recombinants alone (env or env+gag). Despite the induction of vigorous immune responses, 17 of 18 rhesus monkeys became infected on challenge with a low dose of virulent SIVmac. The single protected animal was one of three challenged with homologous cloned SIV exactly matched to the clone used for construction of trivalent vaccinia virus recombinant and particles. Vaccination may have diminished SIV burdens and rates of CD4+ cell declines in some of the animals, but vaccinated/challenge/infected animals eventually developed fatal disease similar to control animals. These results highlight the extreme difficulty in achieving vaccine protection against virulent SIVmac infection even under idealized laboratory conditions.

Limb salvage compared with amputation for osteosarcoma of the distal end of the femur. A long-term oncological, functional, and quality-of-life study

The outcome of treatment of nonmetastatic high-grade osteosarcoma in the distal part of the femur was studied in 227 patients from twenty-six institutions. Eight of the seventy-three patients who had had a limb-salvage procedure and nine of the 115 patients who had had an above-the-knee amputation had a local recurrence, but there was no local recurrence in the thirty-nine patients who had had a disarticulation at the hip. There were no significant differences in the rate of survival or in the duration of the postoperative disease-free period between the three groups. One hundred and nine patients (48 per cent) were alive at an average of eleven years after the operation, and ninety patients (40 per cent) remained continuously disease-free. An additional operation on the limb was necessary more often for patients who had had a limb-salvage procedure than for those who had had an amputation. Function in seventy-eight living patients was assessed with the system of the Musculoskeletal Tumor Society for evaluation of function and by the functional assessment portion of the 1989 scoring system of the Knee Society; the scores were higher for the patients who had had a limb-salvage procedure than for the two groups of patients who had had an amputation. No difference was identified between the groups with regard to the patient's acceptance of the postoperative state, the ability to walk, or the amount of pain. The quality of life was evaluated for twenty-nine patients with a series of complex questionnaires.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular pharmacology of N1- and N8-aziridinyl analogues of spermidine

We have previously described the synthesis and cytotoxic properties of 2 polyamine analogues in which either the N1- or N8-amino group of spermidine was replaced by the alkylating moiety, aziridine. However, the mechanisms by which these aziridinyl analogues of spermidine inhibit cell growth remain unknown. As a result, we have studied: (a) the effect of pretreatment with difluoromethyl ornithine (DFMO) and coincubation with exogenous spermidine on cytotoxicity induced by the aziridinyl spermidines; (b) the reversibility of the cytotoxicity induced by the aziridinyl spermidines; (c) the accumulation of N1- and N8-aziridinyl spermidine by cells and the effects of DFMO on this process; and (d) the impact of N1- and N8-aziridinyl spermidine on cellular polyamine pools and on cellular accumulation of spermidine. The cytotoxicity induced by these 2 aziridinyl derivatives of spermidine [concentration required to inhibit cell growth or incorporation of radiolabeled precursor into trichloroacetic acid-precipitable material by 50% (IC50) N1 = 0.2 microM, IC50 N8 = 0.4 microM)] was potentiated by pretreatment of L1210 cells for 24 h with 100 microM DFMO (IC50 N1 = 0.05 microM, IC50 N8 = 0.15 microM) and was prevented by coincubation with 3.7 microM spermidine (IC50 N1 = 1.1 microM, IC50 N8 = 2.4 microM). In contrast, similar pretreatment with DFMO or coincubation with spermidine had no effect on the cytotoxicity induced by the aziridine-containing alkylating agent, N,N',N"-triethylenethiophosphoramide (thiotepa) (IC50 = 2.4 microM). The cytotoxicity induced by 24-h incubation with either N1- or N8-aziridinyl spermidine was not altered by removal of those compounds and incubating treated cells in medium augmented with 3.7 microM spermidine. However, and as expected, similar maneuvers did not reverse the cell growth-inhibitory effect induced by 24-h incubation with 100 microM DFMO. Cellular accumulation of both N1- and N8-aziridinyl spermidine increased with increasing extracellular concentrations. N1-Aziridinyl spermidine was accumulated to a greater degree than was the N8-analogue, achieving up to 6-fold higher intracellular concentrations at the same extracellular concentration. Cellular accumulation of both aziridinyl compounds was greatly enhanced by 24-h pretreatment with DFMO. Both N1- and N8-aziridinyl spermidine inhibited the uptake of spermidine in a dose-dependent manner. The perturbation of polyamine biochemistry by the test compounds was characterized by their ability to deplete cellular putrescine, as well as spermidine and spermine. These results imply that the cytotoxic mechanism of the aziridinyl spermidine analogues is, to a great extent, dependent on their polyamine nature and may imply selectivity for rapidly growing and neoplastic cells.

Diagnostic strategy for bone and soft-tissue tumors

The diagnostic strategy to be used for a bone tumor depends on the ability of the clinician to make an accurate differential diagnosis on the basis of clinical information and plain radiographs. The clinician must be able to classify the patient as having a non-progressive or a progressive primary benign bone tumor, a primary malignant bone tumor, or a metastatic bone tumor. Only after assignment to one of these four categories can an effective diagnostic strategy ensue. If the clinical and radiographic information favors a diagnosis of malignant or aggressive benign bone tumor, the clinician should refer the patient to an experienced orthopaedic oncologist without performing additional diagnostic tests or a biopsy. If a soft-tissue mass is 5 cm in diameter or larger on physical examination, and especially if it is deep to the fascia, the patient should also be referred to an orthopaedic oncologist, without additional evaluation or biopsy, because of the relatively high probability that the mass is malignant.

New 2-aryl-1,2,3,4-tetrahydropyrido[2,3-d]pyrimidin-4-one derivatives as diuretics

2-Aryl-1,2,3,4-tetrahydropyrido[2,3-d]pyrimidin-4-one derivatives having various substituents at the 4'-position, H or methyl at 1,3-positions and nitro or amino at 6-position were prepared and tested for their diuretic, natriuretic and kaliuretic activities on male Wistar rats at a dosage of 25 mg/kg or less. 2-(3-Pyridyl) derivatives were inactive. 1,3-Dimethyl-6-nitro-2-phenyl derivatives (1) were active depending on the electronic character of the 4'-substituent but at the same time were sodium-sparing. However, 1(H),3(H)-6-nitro-2-phenyl derivatives (2) were generally inactive as diuretics but active as potassium-sparing drugs. 6-Amino-1(H),3(H)-2-phenyl derivatives (4) were active as diuretics depending on dipolar moment of the substituent at the 4'-position, and induced moderate potassium release. The 6-amino-2-(4-trifluoromethylphenyl)-1, 2,3,4-tetrahydropyrido [2,3-d]pyrimidin-4-one (4f) remained active up to a dosage of 3 mg/kg. The structure-activity relationships were carried out in light of the adaptative least squares (ALS) method and discriminant functions for diuretic compounds were established.

Disseminated B virus infection in a cynomolgus monkey

A cynomolgus monkey (Macaca fascicularis) was euthanatized 1 week following dystocia because of severe peritonitis. Histologic examination revealed lesions characteristic of herpesvirus infection in lungs, liver, spleen, bone marrow, uterus, and adrenal gland, and on the serosal surface of intestines, pancreas, and reproductive tract. Immunohistochemical studies on liver and lungs revealed Herpes B-like antigens in the lesions. B virus was isolated from serum. As systemic B-virus infection was not diagnosed before death of the monkey, these findings underscore the need for universal precautions when handling blood, fluids, or tissues from macaques.

Skeletal metastases of unknown origin. A prospective study of a diagnostic strategy

We carried out a prospective study of the effectiveness of a diagnostic strategy in forty consecutively seen patients who had skeletal metastases of unknown origin. The diagnostic strategy consisted of the recording of a medical history; physical examination; routine laboratory analysis; plain radiography of the involved bone and the chest; whole-body technetium-99m-phosphonate bone scintigraphy; and computed tomography of the chest, abdomen, and pelvis. After this evaluation, a biopsy of the most accessible osseous lesion was done. The laboratory values were non-specific in all patients. The history and physical examination revealed the occult primary site of the malignant tumor in three patients (8 per cent): one patient who had carcinoma of the breast; one, of the kidney; and one, of the bladder. Plain radiographs of the chest established the diagnosis of carcinoma of the lung in seventeen patients (43 per cent). Computed tomography of the chest identified an additional six primary carcinomas of the lung (15 per cent). Computed tomography of the abdomen and pelvis established the diagnosis in five patients (13 per cent): three patients who had carcinoma of the kidney; one, carcinoma of the liver; and one, carcinoma of the colon. Examination of the biopsy tissue established the diagnosis in only three additional patients (8 per cent) and confirmed it in eleven others. On the basis of the biopsy alone, we were unable to identify the primary site of the malignant tumor in twenty-six (65 per cent) of the patients. In thirty-four (85 per cent) of the forty patients, the primary site was identified with the use of the diagnostic strategy described here, and only two additional occult malignant tumors were found on follow-up studies. Our diagnostic strategy was simple and highly successful for the identification of the site of an occult malignant tumor before biopsy in patients who had skeletal metastases of unknown origin.

Dedifferentiated chordoma. Response to aggressive chemotherapy in two cases

BACKGROUND

Dedifferentiated chordoma is an unusual and aggressive variant of chordoma which is likely to metastasize. Few reports exist of treatment of these tumors with chemotherapy.

METHODS

In 1988, two patients with dedifferentiated sacral chordomas were seen at the University of Chicago Hospitals. Both developed metastatic disease less than a year after sacral resection and radiation therapy. These patients' diagnoses, courses, and treatments were reviewed along with the literature on chemotherapy in both conventional and dedifferentiated chordomas.

RESULTS

Both patients obtained complete remissions, one to a six-drug regimen and the other to ifosfamide.

CONCLUSIONS

A trial of reasonably aggressive chemotherapy is warranted in patients with metastatic dedifferentiated chordoma. The optimum regimen is unclear, but agents active in high-grade sarcomas are logical choices.

Dedifferentiated chordoma. Response to aggressive chemotherapy in two cases

BACKGROUND

Dedifferentiated chordoma is an unusual and aggressive variant of chordoma which is likely to metastasize. Few reports exist of treatment of these tumors with chemotherapy.

METHODS

In 1988, two patients with dedifferentiated sacral chordomas were seen at the University of Chicago Hospitals. Both developed metastatic disease less than a year after sacral resection and radiation therapy. These patients' diagnoses, courses, and treatments were reviewed along with the literature on chemotherapy in both conventional and dedifferentiated chordomas.

RESULTS

Both patients obtained complete remissions, one to a six-drug regimen and the other to ifosfamide.

CONCLUSIONS

A trial of reasonably aggressive chemotherapy is warranted in patients with metastatic dedifferentiated chordoma. The optimum regimen is unclear, but agents active in high-grade sarcomas are logical choices.

A spontaneous squamous cell carcinoma of the oral cavity in a squirrel monkey (Saimiri sciureus)

A spontaneous squamous cell carcinoma was diagnosed in the oral cavity of an adult female squirrel monkey (Saimiri sciureus). Immunohistochemical analysis of the neoplasm demonstrated cytokeratin and vimentin, but not S100 or desmin in the neoplastic epithelial cells.

An immunohistologic study of granulomatous inflammation in SIV-infected rhesus monkeys

We studied granulomatous inflammation in simian AIDS using histologic, immunohistologic, and in situ hybridization techniques. Complete Freund's adjuvant was used to induce granulomas in two control animals and two macaques infected with simian immunodeficiency virus (SIV) and having low peripheral CD4+ T cell counts. Control animals developed large (> 2 cm diameter) epithelioid granulomas containing CD68+ macrophages (m phi s), epithelioid m phi s and multinucleated giant cells (MNGCs), CD4+ and CD8+ T cells, and small perivascular collections of CD20+ B cells. Lymphocytes rarely expressed proliferating cell nuclear antigen (Ki-67), and only rare endothelial cells expressed vascular cell adhesion molecule 1 (VCAM-1). In contrast, SIV+ animals had smaller (< 0.5 cm diameter) epithelioid granulomas characterized by numerous large, dense CD8+, CD20+ lymphocyte aggregates with prominent local division (Ki-67+). Despite low blood CD4+ T cell numbers, there was a substantial CD4+ T cell infiltrate, accompanied by enhanced endothelial VCAM-1 expression. These granulomas contained no detectable SIV antigen or RNA. Thus, in simian AIDS, experimentally induced granulomatous responses are grossly attenuated, yet associated with increased local endothelial-leukocyte signaling and lymphocyte division.

An SH3-SH2-SH3 protein is required for p21Ras1 activation and binds to sevenless and Sos proteins in vitro

Activation of the sevenless protein-tyrosine kinase is required for the proper specification of R7 photoreceptors in the Drosophila eye. The activation of a Ras protein, p21Ras1, is a crucial early event in the signaling pathway, and constitutive activation of p21Ras1 is sufficient to induce all of the effects of sevenless action. Here we report that another gene, E(sev)2B, required for proper signaling by sevenless encodes a protein of the structure SH3-SH2-SH3. We further provide evidence that the E(sev)2B protein is required for activation of p21Ras1 but not for any subsequent events, and that this protein can bind in vitro to sevenless and to Son of sevenless (Sos), a putative guanine nucleotide exchange factor for p21Ras1. These results suggest that the E(sev)2B protein may act to stimulate the ability of Sos to catalyze p21Ras1 activation by linking sevenless and Sos in a signaling complex. We have renamed the E(sev)2B locus downstream of receptor kinases (drk).

Principles of staging of soft-tissue sarcomas

The TNM staging system is a modus for diagnosis and treatment in which T is the extent of the tumor involvement, N is lymph node involvement, and M is the metastases; this system is supplemented with a histologic malignancy grade. Staging systems identify specific prognostic factors with which to predict clinical outcome. Staging systems are useful for assigning treatment priorities, determining the role of adjuvant therapies, and evaluating clinical investigations. Unfortunately, no universally accepted staging system for soft-tissue sarcomas exists. This is related to the relatively low incidence of sarcomas, the unique and unpredictable behavior of sarcomas, significant disagreement regarding histogenesis and grading, and lack of consensus regarding the value of various prognostic factors. In adults, the two most commonly used staging systems are those developed by the American Joint Committee on Cancer and by Enneking. In children, the Intergroup Rhabdomyosarcoma Study and the International Union Against Cancer have described the systems most commonly used. These systems for soft-tissue sarcomas rely on an ability to accurately determine both the local and distant extent of disease. Advances in the field of computed tomography and magnetic resonance imaging have made this possible. It is likely that a staging system based upon a more sophisticated understanding of the basic biology of sarcomas will become available.

Diagnostic strategy for bone and soft-tissue tumors

The diagnostic strategy to be used for a bone tumor depends on the ability of the clinician to make an accurate differential diagnosis on the basis of clinical information and plain radiographs. The clinician must be able to classify the patient as having a non-progressive or a progressive primary benign bone tumor, a primary malignant bone tumor, or a metastatic bone tumor. Only after assignment to one of these four categories can an effective diagnostic strategy ensue. If the clinical and radiographic information favors a diagnosis of malignant or aggressive benign bone tumor, the clinician should refer the patient to an experienced orthopaedic oncologist without performing additional diagnostic tests or a biopsy. If a soft-tissue mass is five centimeters in diameter or larger on physical examination, and especially if it is deep to the fascia, the patient should also be referred to an orthopaedic oncologist, without additional evaluation or biopsy, because of the relatively high probability that the mass is malignant.

Clinical and pathologic findings in infant rhesus macaques infected with SIVsmm by maternal transmission

Three of 12 infant rhesus macaques became infected at 9 to 12 months of age with SIVsmm through maternal-infant transmission. Clinical problems seen in one or more infants included decreased CD4 cells, hypergammaglobulinemia, diarrhea, weight loss, anemia, bacterial infections, and terminal respiratory and CNS problems. Gross and histologic lesions due to both primary SIV infection and opportunistic infections were observed. The SIV-infected infants had clinical, immunologic, and pathologic similarities to those seen in pediatric HIV infection.

Arteriopathy in macaques infected with simian immunodeficiency virus

BACKGROUND

An arteriopathy characterized by intimal and medial thickening and fibrosis was seen in 19 of 85 rhesus monkeys infected with simian immunodeficiency virus (SIV), a lentivirus with morphologic, genetic, and biologic similarities to HIV-1 and HIV-2.

EXPERIMENTAL DESIGN

All cases of simian AIDS in rhesus monkeys at the New England Regional Primate Research Center, resulting from either experimental or naturally acquired SIV infection, were retrospectively examined for evidence of histopathologic changes to the vasculature. Of the 85 SIV-related deaths recorded in the pathology files to date, tissues from 19 animals were chosen for further study because of thickening, disruption, inflammation, or other abnormality to any layer of the vascular wall. The lesion was characterized by special stains, immunoperoxidase procedures, and ultrastructural examination.

RESULTS

Affected monkeys of both sexes varied in age from 4 months to 17 years at the time of inoculation and survived from 41 days to 4 years after infection. Pulmonary arteries were affected in all 19 animals, while vessels in other parenchymal organs were involved less frequently. In addition to sometimes marked intimal thickening with luminal occlusion, the internal elastic laminae were fragmented and interrupted. Seven of 19 animals had pulmonary thromboses with varying degrees of organization and recanalization. Immunohistochemical studies, special stains, and ultrastructural analyses revealed the thickened intimae to be composed predominantly of collagen, extracellular matrix, and smooth muscle cells. Ultrastructurally, endothelial cells from both early (no intimal thickening) and advanced lesions were plump, vacuolated, and often disorganized and detached from the subendothelial space. Increased numbers of macrophages (CD68+) were found in the adventitia and occasionally in the thickened intima and media. Rare, fully differentiated macrophages (CD68+, 25F9+) were demonstrated in lumina of affected vessels, some of which expressed p27 SIV gag protein. However, the lesion was not uniformly associated with localization of either viral protein or RNA at the site using immunohistochemistry or in situ hybridization, respectively. A similar arterial lesion has been described in children with AIDS.

CONCLUSIONS

The morphologic findings in macaques and their similarity to arteriosclerotic changes induced by experimental endothelial damage in other species collectively suggest that arteriopathy in AIDS may represent a manifestation secondary to primary endothelial injury.

The growth inhibitory action of melatonin on human breast cancer cells is linked to the estrogen response system

The pineal hormone, melatonin, was examined for its capacity to modulate the proliferation of a panel of human breast cancer cell lines. Melatonin inhibited, to a varying extent, the proliferation of all three estrogen-responsive cell lines, but had no effect on estrogen-insensitive breast tumor cell lines. Melatonin was also able to specifically block estrogen-induced proliferation in MCF-7 breast cancer cells. However, this action was abolished in the presence of tamoxifen. Therefore, it appears that the antiproliferative effects of melatonin are mediated through the estrogen-response pathway.

Clinical pharmacokinetics of R(+)- and S(-)-mepivacaine after high doses of racemic mepivacaine with epinephrine in the combined psoas compartment/sciatic nerve block

The purpose of this study was to investigate the pharmacokinetics of R(+)- and S(-)-mepivacaine in 10 male patients after injection of a high dose (731 mg) of racemic R,S-mepivacaine for a combined psoas compartment/sciatic nerve block. Arterial blood samples were taken, and the plasma concentrations of the stereoisomers R(+)- and S(-)-mepivacaine were measured by means of high-performance liquid chromatography (HPLC) with a Chiral AGP column. The S(-) isomer reached higher plasma concentrations than the R(+) isomer. The maximal plasma concentration (Cmax) of R(+) was 1.54 +/- 0.34 micrograms/mL, whereas that of the S(-) isomer was 2.34 +/- 0.51 micrograms/mL (P = 0.00050). The time at which Cmax was reached (Tmax) was identical for both isomers. The area under the plasma concentration-time curve from t = 0 to infinity (AUC infinity) of S(-)-mepivacaine was almost double that of R(+)-mepivacaine. The elimination half-life (T1/2) was identical for both isomers (3 h), which means that the calculated total body clearance and the calculated steady-state volume of the distribution of R(+) are, respectively, 1.7 and 1.5 times larger than that of the S(-) isomer. We conclude that the plasma concentrations of the S(-)-mepivacaine isomer were higher than those of the R(+) isomer because of a smaller volume of distribution and a slower total body clearance.

Simian virus 40-induced disease in rhesus monkeys with simian acquired immunodeficiency syndrome

Simian virus 40 (SV40) disease was diagnosed in four rhesus monkeys that died with SIV-induced acquired immunodeficiency syndrome (AIDS). One juvenile monkey seroconverted for SV40 6 months after inoculation with SIV and developed severe bilateral tubulointerstitial nephritis. In contrast, progressive multifocal leukoencephalopathy (PML) occurred in two adult monkeys that were seropositive for SV40 before SIV inoculation, as well as a third adult that was naturally infected with SIV and seropositive for SV40 5 years before death. Large intranuclear inclusions containing abundant polyomavirus particles were limited to either renal tubular epithelial cells or oligodendrocytes. In situ DNA hybridization for SV40 large T antigen further demonstrated that SV40 nucleic acid was localized to either kidney or brain tissue. By immunohistochemical analysis, areas of central nervous system inflammation and demyelination were shown to contain CD68+ macrophages (gitter cells), aggregates of CD8+ T lymphocytes, and numerous gemistocytic astrocytes that labeled for glial fibrillary acidic protein. These observations indicate that rhesus monkeys with SIV-induced AIDS are predisposed to polyomaviral disease, in which SV40 nucleic acid is observed in renal tissue in primary infections and brain tissue after viral reactivation. Furthermore, this organ-specific replication suggests that tissue-tropic strains of SV40 may develop in immunodeficient monkeys.

Evaluation, prognosis, and medical treatment considerations of metastatic bone tumors

Metastatic cancer can cause severe pain and disability. Metastases can occur in any bone, but usually are located in the axial or proximal appendicular skeleton. The most frequently encountered primary tumors that spread to bone are those of the prostate, breast, kidney, lung, and thyroid. When the origin of the primary cancer is known, skeletal metastases are more often from breast or prostate. When the primary site is unknown, the lung and kidney should be suspected as sites of origin. The nonoperative management of skeletal metastases from multiple myeloma and from carcinomas of the prostate, breast, kidney, lung, and thyroid are discussed.

Pathologic features of SIV-induced disease and the association of macrophage infection with disease evolution

Since the original isolation of simian immunodeficiency virus (SIV) from a macaque with an AIDS-like disease, numerous studies have demonstrated the close biologic and genetic relationship of the SIVs to the HIVs. Probably most important, the clinical spectrum of disease associated with SIVmac/SIVsmm infection in rhesus monkeys is strikingly similar to AIDS in HIV-1-infected human beings. Herein are summarized the pathologic features of SIVmac-induced disease in a cohort of rhesus monkeys, with special reference to the role of infected macrophages in the development of AIDS-related manifestations.