Genomic characterization of HER2-positive breast cancer and response to neoadjuvant trastuzumab and chemotherapy-results from the ACOSOG Z1041 (Alliance) trial

Background

HER2 (ERBB2) gene amplification and its corresponding overexpression are present in 15-30% of invasive breast cancers. While HER2-targeted agents are effective treatments, resistance remains a major cause of death. The American College of Surgeons Oncology Group Z1041 trial (NCT00513292) was designed to compare the pathologic complete response (pCR) rate of distinct regimens of neoadjuvant chemotherapy and trastuzumab, but ultimately identified no difference.

Patients and methods

In supplement to tissues from 37 Z1041 cases, 11 similarly treated cases were obtained from a single institution study (NCT00353483). We have extracted genomic DNA from both pre-treatment tumor biopsies and blood of these 48 cases, and performed whole genome (WGS) and exome sequencing. Coincident with these efforts, we have generated RNA-seq profiles from 42 of the tumor biopsies. Among patients in this cohort, 24 (50%) achieved a pCR.

Results

We have characterized the genomic landscape of HER2-positive breast cancer and investigated associations between genomic features and pCR. Cases assigned to the HER2-enriched subtype by RNA-seq analysis were more likely to achieve a pCR compared to the luminal, basal-like, or normal-like subtypes (19/27 versus 3/15; P = 0.0032). Mutational events led to the generation of putatively active neoantigens, but were overall not associated with pCR. ERBB2 and GRB7 were the genes most commonly observed in fusion events, and genomic copy number analysis of the ERBB2 locus indicated that cases with either no observable or low-level ERBB2 amplification were less likely to achieve a pCR (7/8 versus 17/40; P = 0.048). Moreover, among cases that achieved a pCR, tumors consistently expressed immune signatures that may contribute to therapeutic response.

Conclusion

The identification of these features suggests that it may be possible to predict, at the time of diagnosis, those HER2-positive breast cancer patients who will not respond to treatment with chemotherapy and trastuzumab.

ClinicalTrials.gov identifiers

NCT00513292, NCT00353483.

Abstract PD6-02: The genomics of response to neoadjuvant trastuzumab and chemotherapy in HER2-positive breast cancer – Results from the ACOSOG Z1041 (Alliance) trial

Support: Alliance U10CA180821; Alliance Statistical Center grant U10CA180882; ACOSOG grant U10CA76001

HER2 gene amplification and its corresponding overexpression are present in approximately 12% of invasive breast cancers. While HER2-targeted agents (e.g. trastuzumab, pertuzumab, and lapatinib) are effective treatments, resistance remains a major cause of death from HER2-positive breast cancer. Mechanisms of resistance are poorly understood. Without a molecular understanding of these mechanisms, therapeutic advances will be delayed. We have generated molecular profiles of primary HER2-positive breast cancers treated on a neoadjuvant clinical trial, and compared features associated with response to treatment.

The American College of Surgeons Oncology Group (ACOSOG) Z1041 trial in HER2-positive breast cancer was designed to compare the pathologic complete response (pCR) rate of a regimen of paclitaxel and trastuzumab, followed by trastuzumab administered with fluorouracil, epirubicin, and cyclophosphamide (FEC-75) to a regimen of FEC-75 alone followed by paclitaxel and trastuzumab. The trial identified no difference in pCR rates between the regimens (Buzdar et al., The Lancet Oncology 2013). In supplement to the tissues obtained from 37 of the patients enrolled in the Z1041 trial, an additional 11 cases were obtained from a single institution study (201101961) of patients treated with neoadjuvant trastuzumab that had pre-treatment core biopsies suitable for genomic studies.

We have extracted genomic DNA from both pretreatment tumor biopsies and blood samples of these 48 patients and performed whole genome (WGS) and exome sequencing. Coincident with these efforts, we have extracted high quality RNA from 42 of the 48 biopsies, and have processed RNA-seq profiles of the tumors. Among patients in this cohort, 24 (50%) achieved a pCR. Because no difference was observed between arms of the Z1041 trial, patients with or without a pCR were directly compared without adjusting for treatment regimen.

On average, each tumor and normal sample pair were sequenced to a depth of 49.4x and 32.5x by WGS respectively. In total, 15,027 candidate somatic variants were identified in known genes, including 11,606 missense, 860 nonsense, and 418 frameshift insertions or deletions. Preliminary results identified mutations in HER2 that were associated with the failure to achieve pCR in several cases. Furthermore, tumors assigned to the HER2-enriched subtype by RNA-seq analysis were more likely to achieve a pCR (19 compared to 8) than tumors with genomic features indicative of either the luminal or basal-like subtypes (3 compared to 12); a significant difference in the proportion of cases that achieve pCR (Fisher's exact test p-value = 0.0032). The identification of these features suggests that it may be possible to predict, at the time of diagnosis, those patients who will not respond to the current standard of care for HER2-positive breast cancer.

Citation Format: Lesurf R, Griffith O, Griffith M, Watson MA, Hoog J, Ellis MJ, Ota D, Suman VJ, Meric-Bernstam F, Leitch AM, Boughey JC, Unzeitig G, Buzdar AU, Hunt KK, Mardis ER. The genomics of response to neoadjuvant trastuzumab and chemotherapy in HER2-positive breast cancer – Results from the ACOSOG Z1041 (Alliance) trial. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr PD6-02.

ACOSOG Z0010: A multicenter prognostic study of sentinel node (SN) and bone marrow (BM) micrometastases in women with clinical T1/T2 N0 M0 breast cancer

CRA504

Background: SN biopsy (SNB) with immunohistochemistry (IHC) of histologically negative SN identifies metastases (mets) not seen by standard histology. The impact of IHC-detected BM mets has been reported in several large single-institution studies. 5,539 patients (pts) were entered into this prospective multicenter observational study to determine the clinical significance of SN and BM mets.

Methods: Patients underwent lumpectomy and SNB with bilateral iliac crest BM aspiration. BM and histologically negative SN were evaluated with IHC in a central laboratory (results not clinically reported). Overall survival (OS), disease-free survival, and locoregional recurrence were determined. Results with OS (the primary endpoint) are reported here.

Results: SN were successfully identified in 5,184 of 5,485 pts (94.5%). Histologic SN mets were found in 1,239 pts (23.9%). IHC detected an additional 350 pts (10.5%) with SN mets. BM mets were identified by IHC in 105 of 3491 examined (3.0%). 5-yr overall survival is shown in the Table . BM IHC positivity significantly predicted decreased OS (p=0.015). A multivariable analysis that included SN and BM status, ER, PR, grade, size, and age showed that neither IHC detected mets in SN (p=0.66) or BM (p=0.08) were independent predictors of OS, although BM status showed a strong trend.

Conclusions: The detection of BM mets by IHC in pts with clinical T1/2 N0M0 breast cancer identifies those pts at significantly increased risk for death; the impact of BM mets on outcome supports and confirms prior studies. In this study, SN IHC-detected mets appear to have no significant impact on OS. The routine examination of SN by IHC is not supported in this patient population by this study.

[Table: see text]

[Table: see text]

ACOSOG Z0011: A randomized trial of axillary node dissection in women with clinical T1-2 N0 M0 breast cancer who have a positive sentinel node

CRA506

Background: Sentinel node biopsy (SNB) eliminates the need for axillary dissection (ALND) in patients whose sentinel node (SN) is tumor-free. However, completion ALND remains the gold standard for patients with a tumor-involved sentinel node. ALND achieves regional control, but its effect on survival remains controversial. The main objective of ACOSOG Z0011 was to compare outcomes of patients with hematoxylin and eosin (H&E) detected metastasis in SN managed with or without ALND and no axillary irradiation.

Methods: Clinically node-negative patients who underwent SN biopsy and had 1 or 2 SN with metastases detected by H&E were randomized to ALND or no further axillary specific treatment. All patients were treated with lumpectomy and opposing tangential field irradiation. Adjuvant systemic therapy was at the discretion of their physicians. Overall survival (OS), disease-free survival (DFS), and locoregional control were evaluated.

Results: 446 patients were randomized to SNB alone and 445 to SNB plus ALND. Patients treated with SNB alone were similar to those treated with SNB + ALND with respect to age, tumor size, Bloom-Richardson score, estrogen receptor status, adjuvant systemic therapy, tumor type, and T stage. Patients randomized to SNB alone had a median of two lymph nodes removed whereas patients randomized to ALND had a median of 17 lymph nodes removed. 17.6% of ALND patients had 3 or more involved nodes compared to 5.0% of SNB patients (p < 0.001). Median follow-up is 6.2 years. 5-year in breast recurrence after ALND was 3.7% compared to 2.1% for SNB (p = 0.16) while 5-year nodal recurrence was 0.6% compared to 1.3% (p = 0.44) respectively. The five-year OS for patients undergoing SNB + ALND is 91.9% compared to 92.5% for SNB alone (p = 0.24), and DFS is 82.2% compared to 83.8% respectively (p = 0.13).

Conclusions: Despite the widely held belief that ALND improves survival, no significant difference was recognized by this study of SN node-positive women. Although the study closed early because of low accrual/event rate, it is the largest phase III study of ALND for node-positive women, and it demonstrates no trend toward clinical benefit of ALND for patients with limited nodal disease.

[Table: see text]

Cell-based breast cancer risk stratification based on DNA methylation in fine needle aspiration samples

1508

Background: Tumor suppressor gene (TSG) methylation is identified in nearly all breast cancers, but rarely in histologically normal breast tissue from wonen unaffected with breast cancer. Its occurrence in high risk preneoplasia and in benign breast tissue adjacent to breast cancer suggests that it may represent a high risk field change that could be exploited for cell-based breast cancer risk stratification. Methods: TSG methylation was measured by quantitative methylation-specific real time PCR in 53 breast tumor fine needle aspiration (FNA) biopsies, 84 cellular random periareolar FNAs (RP-FNA) ipsilateral or contralateral to these cancers, 36 cellular RP- FNAs from unaffected women at high risk for breast cancer by the Gail model, and 95 cellular RP-FNAs from unaffected women at lower risk by the Gail model. Results: The breast tumors showed a high frequency of TSG methylation: RASSF1A 80%, HIN-1 65%, Cyclin D2 60%, RAR-β2 53%, and APC 47%. In general, RP-FNA samples from cancer patients and Gail high risk patients showed a greater frequency of methylation than samples from Gail lower risk patients: RASSF1A 43% vs. 21%, P = 0.001, HIN-1 32% vs. 20%, P = 0.05; Cyclin D2 18% vs. 9%, P = 0.10; RAR-β2 21% vs. 18%, P = 0.68; and APC 25% vs. 16%, P = 0.17. Twelve of 215 RP-FNA samples (5%) showed very high levels of methylation (>10% methylation for two or more genes). Only two of these samples were from women classified as lower risk by the Gail model. Methylation frequencies were entirely independent of cell yields but the frequency of RASSF1A methylation increased with increasing Masood scores (P = 0.05). Methylation of RASSF1A in one breast was highly predictive of RASSF1A methylation in the opposite breast (P < 0.0001). Conclusions: TSG methylation appears to be a breast cancer risk-associated field change that can be quantified in RP-FNA samples. RASSF1A methylation occurs frequently in benign breast epithelium, provides reasonable discrimination between high and lower risk breasts (O.R. = 2.0), is related to cytological atypia, and may be an early marker of a methylator phenotype. Quantification of TSG methylation in RP-FNA samples may provide a valuable surrogate endpoint biomarker for Phase II prevention trials.

No significant financial relationships to disclose.

Factors influencing accrual to ACOSOG Z0011, a randomized phase III trial of axillary dissection vs. observation for sentinel node positive breast cancer

601

Background: The American College of Surgeons Oncology Group opened a phase III randomized trial to assess the value of axillary node dissection (ALND) after positive sentinel node biopsy (SNB). After 5.5 years, the trial closed due to poor accrual with only 891 patients of the planned 1900 accrued. The purpose of the current analysis is to assess factors impacting accrual to Z0011. Methods: Women having SNB for T1 or T2 breast cancer were eligible for participation in the Z0010 trial to assess the significance of micrometastases identified by immunohistochemistry. If the SN was positive for metastasis by H&E, the patient was eligible for randomization on Z0011 trial. Intraoperative (IOR) and postoperative randomization were allowed. Patients having SNB outside of the Z0010 trial were eligible. Results: 1003 patients from the Z0010 trial were eligible for randomization on Z0011. Of these, only 37% were entered in Z0011. Z0010 participants accounted for 42% of patients in Z0011. 16% of patients not randomized refused ALND. 69% of those not randomized had ALND. 67% of these had no additional positive nodes. Only 14% had ≥ 4 positive nodes. Enrollment of eligible Z0010 patients varied by type of institution: 25% at academic sites, 42% at teaching affiliated and 53% at community (p < 0.0001). By geographic region, sites in the South entered 42% of eligible patients compared with 24–36% in other geographic regions (p=0.0027). Only 32% of patients were consented for IOR based on frozen section of the SN. Sites in the South and West were less likely to use IOR (25% and 28%) compared to Northeast and Midwest (45% and 46%) (p < 0.0001). 110 sites participated in Z0011, yet 48% of patients were enrolled by 10% of sites. Conclusions: Failure of this important trial to accrue as planned is likely related to the clinical bias of physicians and patients to standard ALND. Yet, 2/3 of patients had no additional positive nodes and extensive nodal disease was infrequent. While it was thought that IOR might improve accrual to Z0011, the most successful sites were less likely to use this approach. Community surgeons were most successful in randomizing patients.

[Table: see text]

Assessment of tumor suppressor gene methylation for breast cancer risk screening

1004

Background: Tumor suppressor gene (TSG) methylation is frequently detected in benign proliferative breast tissue suggesting that it occurs early in breast carcinogenesis. If it can be screen-detected and is associated with breast cancer risk it could be exploited for breast cancer prevention. Methods: Nipple duct lavage (NDL) samples, obtained from 150 women selected to represent a wide range of breast cancer risk, were evaluated by quantitative methylation-specific real time PCR. High risk breasts were defined as those contralateral to a breast cancer (N = 63) and those of women with a 5-year Gail risk ≥ twice the age- and race-matched general population risk (N = 64). The prevelence of TSG methylation and marked atypia was compared for high risk and lower risk breasts using Chi-square. Data for breasts ipsilateral to a breast cancer are shown for comparison, but not included in the calculations for the high risk category. Results: Samples with adequate cellularity were obtained for 219 breasts (76%). The proportion of healthy breasts with ≥ 1% of the gene copies methylated was 13% for Cyclin D2, 19% for APC, 19% for HIN-1, 16% for RASSF1A, and 9% for RAR-beta. RAR-beta provided the best risk discrimination as 15% of high risk breasts were methylated at a level that exceeded the 95th percentile of the lower risk breasts (0.9% of gene copies methylated, P = 0.05). For the table , methylation fractions for all five genes were summed and the threshold for classifying a breast as positive was set to the 95th percentile of the lower risk breasts (methylation sum = 25.0%). Both methylation and marked atypia provide some discrimination between high and lower risk breasts; the combination, however, provides the best discrimination (24% marker positive for high risk versus 9% for lower risk, P = 0.02). Conclusions: TSG methylation in NDL samples is a marker of breast cancer risk that is complementary to cytology.

[Table: see text]

[Table: see text]

MRI vs. histologic measurement of breast cancer following chemotherapy: comparison with x-ray mammography and palpation

Twenty consecutive patients with breast cancer were evaluated following chemotherapy using MRI to assess the size of cancer residua and compare these data with subsequent histologic measurements of the viable tumor. This retrospective study also involved assessment of the preoperative size of the malignancy as determined by physical exam and x-ray mammogram. These values were later compared with the histology. The tumor size correlation coefficient between MRI and pathologic analysis was the highest, at 0.93. Physical exam and x-ray mammography (available for 17 patients) produced correlation coefficients of 0.72 and 0.63, respectively, compared to histologic measurement. The accuracy of MRI did not vary with the size of cancer residua. MRI is an accurate method for preoperative assessment of breast cancer residua following chemotherapy. J. Magn. Reson. Imaging 2001;13:868-875.

Breast cancer: screening and early detection

A comprehensive program for breast cancer screening and early detection has a number of components. First, an understanding of the magnitude of the breast cancer problem and the natural history of breast cancer is essential. Appropriate screening guidelines must be identified and adopted into practice. Screening recommendations must be promoted actively. While breast cancer screening guidelines can be applied broadly to the general population, patients who are at increased risk must be identified through formal risk assessment. For those at increased risk, earlier screening and prevention strategies can be recommended. Physicians must be prepared to manage the abnormalities identified in screening and make appropriate referrals for treatment. Finally, patients identified with cancer must be staged accurately, as this staging will determine the prognosis.

Breast cancer screening: success amid conflict

In randomized trials, screening mammography has been shown to reduce breast cancer mortality. There has been controversy, however, about the segment of the population that should be screened and the frequency at which screening should occur. This article details these controversial issues. The benefits that have been realized from mammography screening in overall breast cancer mortality and diagnosis of earlier stage cancers are also reviewed.

Characterization of paired tumor and non-tumor cell lines established from patients with breast cancer

The goal of our study was to develop a panel of tumor cell lines along with paired non-malignant cell lines or strains collected from breast cancers, predominantly primary tumors. From a total of 189 breast tumor samples consisting of 177 primary tumors and 12 metastatic tissues, we established 21 human breast tumor cell lines that included 18 cell lines derived from primary tumors and 3 derived from metastatic lesions. Cell lines included those from patients with germline BRCA1 and FHIT gene mutations and others with possible genetic predisposition. For 19 tumor cell lines, we also established one or more corresponding non-malignant cell strains or B lymphoblastoid (BL) lines, which included 16 BL lines and 7 breast epithelial (2) or stromal (5) cell strains. The present report describes clinical, pathological and molecular information regarding the normal and tumor tissue sources along with relevant personal information and familial medical history. Analysis of the breast tumor cell lines indicated that most of the cell lines had the following features: they were derived from large tumors with or without axillary node metastases; were aneuploid and exhibited a moderate to poorly differentiated phenotype; were estrogen receptor (ER)- and progesterone receptor (PR)-negative; and overexpressed p53 and HER2/neu proteins. Of 13 patients with primary breast cancers receiving curative intent mastectomies, 7 were dead after a mean period of 10 months. Our panel of paired tumor and non-malignant cell lines should provide important new reagents for breast cancer research.

American Cancer Society guidelines for the early detection of breast cancer: update 1997

The American Cancer Society (ACS) convened a workshop in March 1997 to consider new scientific findings related to breast cancer screening and to determine whether these findings warrant a change in the existing ACS guidelines. The meeting was timed so that participants could benefit from new data related to screening women aged 40 to 49 years. A recommendation based on the new data and subsequently approved by the ACS Board of Directors is reported.

Controversies in breast cancer screening

Because breast cancer is the most common cancer occurring in women in the United States, early detection of breast cancer through screening mammography, physician clinical examination, and breast self-examination has been recommended. However, despite admonitions to physicians and patients to be aggressive in their screening efforts, there has been continued controversy regarding appropriate guidelines for screening. In December 1993, the National Cancer Institute announced that it could no longer recommend routine mammographic screening for women age 40-49 years, which it had previously supported along with other medical organizations. This change in policy, along with data from the Canadian National Breast Screening Study showing an increased mortality rate for screened women, created confusion for physicians and patients alike. The controversy about screening guidelines has created many practical concerns for the physicians involved in the primary health care of women. In the current paper, the author discussed the development of screening guidelines and the current recommendations of various medical organizations and reviewed the data from studies supporting and challenging the current guidelines, with a focus on screening guidelines for women age 40-49 and the elderly. Recommendations are made for physicians on how to communicate with patients regarding screening controversies.

Breast cancer in a county hospital population: impact of breast screening on stage of presentation

BACKGROUND

Indigent patients in a county hospital setting typically present with breast cancer at a later stage than do patients in the private sector. In the early 1980s, 50% of all breast cancers diagnosed in our county hospital were stages III and IV. This contrasted markedly with the findings of an American College of Surgeons study, which showed < 15% of breast cancers diagnosed as stages III and IV.

METHODS

Recognizing this disparity, we instituted a breast screening project in the county teaching hospital targeted at women who routinely received medical care in the county hospital clinics. Between 1985 and 1992, 14,567 mammograms were performed.

RESULTS

Two hundred eighty-nine breast biopsies were performed and 76 cancers were identified (26%). Ninety-five patients advised to have surgical consultation for biopsy declined further evaluation. The stage distribution of cancers diagnosed was as follows: stage 0, 20%; stage I, 43%; stage II, 28%; stage III, 8%; and stage IV, 1%. This compares favorably with National Cancer Data Base statistics for 1988. In contrast, symptomatic nonscreened patients diagnosed at the county hospital in 1992 presented at a significantly more advanced stage: stage 0, 1%; stage I, 14%; stage II, 45%; stage III, 26%; and stage IV, 13%.

CONCLUSIONS

Mammographic screening has lowered the stage of cancers diagnosed in the screened indigent population. However, a significant percentage of patients are presenting to our hospital with stage III and IV disease. Problems identified in the screening project included noncompliance with recommendations for follow-up of abnormal studies and noncompliance with appointments. In order to broaden the impact of our breast screening project, we have instituted outreach programs with community-based clinics and the American Cancer Society.

Multimodality treatment of locally advanced breast carcinoma

Forty patients with 41 locally advanced breast lesions at stages IIIA and IIIB and the inflammatory stage were treated with combined-modality therapy from July 1980 to August 1985. Treatment included induction chemotherapy consisting of three cycles of fluorouracil, doxorubicin hydrochloride, and cyclophosphamide, followed by mastectomy in those patients whose lesions were operable (n = 28), and resumption of chemotherapy. Nine patients received postoperative radiation therapy. The mean follow-up was 34 months. Greater than 50% reduction in tumor size was achieved in 72% of patients after three cycles of chemotherapy. Overall, local control was achieved in 85% of patients with 59% survival and 53% disease-free survival, while 10% of patients developed local recurrences. Excluding lymphedema of the upper extremity (n = 2) and inflammatory carcinomas (n = 4), local control was achieved in 96% of patients, with 75% survival and 68% disease-free survival, while 4% of patients developed local recurrences. The rate of disease-free survival was 71% in patients with partial response to chemotherapy, contrasted with 43% in patients who did not respond or only minimally responded to chemotherapy. Actuarial five-year survival, based on life-table analysis, was calculated to be 46% for the group overall, 58% for the group excluding lymphedema of the upper extremity and inflammatory carcinoma, and 56% for the 28 patients undergoing mastectomy.

Detection of tumour associated antigen in eluates from protein A columns used for ex vivo immunoadsorption of plasma from melanoma patients by radioimmunoassay

Tumour associated antigen (TAA) of defined specificity and anti-TAA antibodies were isolated by elution with 0.1 M glycine-HCl buffer (pH 3.5) and 2.5 M MgCl2 from non-viable Staphylococcus aureus used in ex vivo immunoadsorption of plasma from four melanoma patients. The anti-TAA antibody activity in the MgCl2 eluate was determined by its ability to bind a melanoma 125I-TAA. The melanoma 125I-TAA was isolated and purified from the spent culture medium of a human melanoma cell line. The activity and specificity of TAA in the glycine-HCl eluates were determined by competitive inhibition in a radioimmunoassay in which melanoma 125I-TAA and an allogeneic antiserum obtained from a melanoma patient were used as the reagents. Results indicated that 0.04-0.81% of the total protein contained in the glycine-HCl eluates was TAA. The proportion of TAA to total protein in these eluates varied from patient to patient and treatment to treatment. Inhibition by the glycine-HCl eluates in the competitive radioimmunoassay was dose-dependent. Similarly, binding of melanoma 125I-TAA in a direct radioimmunoassay decreased with decreasing amounts of the anti-TAA antibody fraction. Quantitative analysis revealed that the MgCl2 eluates contained anti-TAA protein at levels ranging from 0.15 to 5.78% of total protein. Because both TAA and anti-TAA activities were found in eluates from S. aureus (protein A positive) used for immunoadsorption of plasma from melanoma patients, and because melanoma 125I-TAA isolated and purified from a human melanoma cell line did not bind to protein A directly, the results indicated that TAAs immunologically similar to the melanoma TAA were circulating in the form of immune complexes in plasma of four patients with melanoma and that these complexes could be removed from plasma by ex vivo immunoadsorption.

Nature of antigens and antibodies in immune complexes isolated by staphylococcal protein A from plasma of melanoma patients

Immune complexes (IC) were isolated from plasma of melanoma patients by absorption to staphylococcal protein A and subsequent elution with MgCl2. The isolated ICs were purified by precipitation with polyethylene glycol and sucrose density gradient ultracentrifugation after radioiodination with 125I. The purified ICs were dissociated and radiolabeled antigen/antibody components were separated by ultracentrifugation at low pH (2.6). Under these conditions, about 72% radioactivity of the purified IC remained in the light-density region as a wide band. After neutralization, 26%-60% radioactivity in the region of 5S sedimentation bound to immobilized autologous immunoglobulins, as opposed to a maximum of 23% to immobilized immunoglobulins from human normal serum. Significant levels (73%-77%) of radioactivity in 7S region bound to rabbit anti-human IgG immunobeads. Immunoprecipitation of the antigen fraction by allogeneic anti-melanoma and rabbit anti-melanoma antibodies followed by SDS-polyacrylamide gel electrophoresis revealed the presence of a fetal antigen (FA) and a melanoma tumor-associated antigen (TAA). In addition, the presence of auto-antigen(s) was indicated by using autologous antibody in immunoprecipitation. Immunoglobulins (IgG) isolated from purified IC bound to cultured melanoma, sarcoma, and normal fibroblasts, although the binding to sarcoma and normal fibroblasts could be inhibited by preincubation of isolated IgG with soluble FA but not with soluble melanoma TAA. Thus, results of this investigation provide evidence that circulating IC in melanoma patients are composed of at least IgG and different antigens, and some of these antigens are produced by their tumor.