American Society of Clinical Oncology technology assessment of pharmacologic interventions for breast cancer risk reduction including tamoxifen, raloxifene, and aromatase inhibition

OBJECTIVE

To update an evidence-based technology assessment of chemoprevention strategies for breast cancer risk reduction. POTENTIAL INTERVENTIONS: Tamoxifen, raloxifene, aromatase inhibition, and fenretinide.

OUTCOMES

Outcomes of interest include breast cancer incidence, breast cancer-specific survival, overall survival, and net health benefit.

EVIDENCE

A comprehensive, formal literature review was conducted for relevant topics. Testimony was collected from invited experts and interested parties. The American Society of Clinical Oncology (ASCO) prescribed technology assessment procedure was followed.

VALUES

More weight was given to published randomized trials. BENEFITS/HARMS: A woman's decision regarding breast cancer risk reduction strategies is complex and will depend on the importance and weight attributed to information regarding both cancer- and noncancer-related risks and benefits.

CONCLUSIONS

For women with a defined 5-year projected breast cancer risk of > or= 1.66%, tamoxifen (at 20 mg/d for 5 years) may be offered to reduce their risk. Risk/benefit models suggest that greatest clinical benefit with least side effects is derived from use of tamoxifen in younger (premenopausal) women (who are less likely to have thromboembolic sequelae and uterine cancer), women without a uterus, and women at higher breast cancer risk. Data do not as yet suggest that tamoxifen provides an overall health benefit or increases survival. In all circumstances, tamoxifen use should be discussed as part of an informed decision-making process with careful consideration of individually calculated risks and benefits. Use of tamoxifen combined with hormone replacement therapy or use of raloxifene, any aromatase inhibitor or inactivator, or fenretinide to lower the risk of developing breast cancer is not recommended outside of a clinical trial setting. This technology assessment represents an ongoing process and recommendations will be updated in a timely matter.

VALIDATION

The conclusions were endorsed by the ASCO Health Services Research Committee and the ASCO Board of Directors.

American Society of Clinical Oncology technology assessment on the use of aromatase inhibitors as adjuvant therapy for women with hormone receptor-positive breast cancer: status report 2002

OBJECTIVE

To conduct an evidence-based technology assessment to determine whether the routine use of anastrozole or any of the aromatase inhibitors in the adjuvant breast cancer setting is appropriate for broad-based conventional use in clinical practice. POTENTIAL INTERVENTIONS: Anastrozole, letrozole, and exemestane.

OUTCOMES

Outcomes of interest include breast cancer incidence, breast cancer-specific survival, overall survival, and net health benefit.

EVIDENCE

A comprehensive, formal literature review was conducted for relevant topics and is detailed in the text. Testimony was collected from invited experts and interested parties. The American Society of Clinical Oncology (ASCO)-prescribed technology assessment procedure was followed. BENEFITS/HARMS: The ASCO panel recognizes that a woman and her physician's decision regarding adjuvant hormonal therapy is complex and will depend on the importance and weight attributed to information regarding both cancer and non-cancer-related risks and benefits.

CONCLUSION

The panel was influenced by the compelling, extensive, and long-term data available on tamoxifen. Overall, the panel considers the results of the Arimidex (anastrozole) or Tamoxifen Alone or in Combination (ATAC) trial and the extensive supporting data to be very promising but insufficient to change the standard practice at this time (May 2002). A 5-year course of adjuvant tamoxifen remains the standard therapy for women with hormone receptor-positive breast cancer. The panel recommends that physicians discuss the available information with patients, and, in making a decision, acknowledge that treatment approaches can change over time. Individual health care providers and their patients will need to come to their own conclusions, with careful consideration of all of the available data. (Specific questions addressed by the panel are summarized in Appendix 3.)

VALIDATION

The conclusions of the panel were endorsed by the ASCO Health Services Research Committee and the ASCO Board of Directors.

Side effects of chemotherapy and combined chemohormonal therapy in women with early-stage breast cancer

The decision to receive chemotherapy or chemohormonal therapy involves careful consideration of both the potential benefits and possible risks of therapy. There are substantial short- and long-term side effects from chemotherapy. By convention, short-term side effects include those toxic effects encountered during chemotherapy, while long-term side effects include later complications of treatment arising after the conclusion of adjuvant chemotherapy. These side effects vary, depending on the specific agents used in the adjuvant regimen as well as on the dose used and the duration of treatment. There is also considerable variability in side effect profile across individuals. This review will focus on the short- and long-term toxicity seen with the most commonly used adjuvant chemotherapy and chemohormonal therapy regimens.

Gemcitabine-induced radiation recall

PURPOSE

To study and report 6 patients with radiation recall in unique sites, secondary to gemcitabine chemotherapy.

METHODS AND MATERIALS

The clinical presentations and outcomes of 6 patients with radiation recall secondary to gemcitabine chemotherapy were retrospectively analyzed over the course of a 1-year period.

RESULTS

Radiation recall reactions were seen in the central nervous system, skin, gastrointestinal tract, and in the lymphatic and musculoskeletal systems. The time between initiation of radiation and recall of the radiation phenomenon ranged from 3 weeks to 8 months from the time gemcitabine was initiated. The usual dosage of gemcitabine in these cases was 1000 mg/m(2) given on a weekly basis. No radiation therapy was given concomitantly with gemcitabine. Treatment of the recall reaction consisted of discontinuing gemcitabine and initiating steroid therapy, supportive therapy, and/or nonsteroidal anti-inflammatory agents. Minimal improvement was seen in 3 out of 6 patients, and resolution of the radiation recall was seen in 3 out of 6 patients. A comprehensive review of the literature revealed that radiation recall with gemcitabine has been related to skin reactions only; no previous cases of radiation recall occurring in the central nervous system have been reported with any chemotherapy agent.

CONCLUSION

Radiation recall from gemcitabine chemotherapy is rare, but can potentially arise in any site that has been previously irradiated. Treating physicians must be aware of this potential toxicity from gemcitabine and radiation and discontinue the gemcitabine if radiation recall is observed.

HER2 overexpressing metastatic breast cancer

More than 40,000 women in the United States die each year from metastatic breast cancer. Elucidation of HER2 and its role in malignant transformation has helped define a subset of aggressive breast cancer that may be relatively resistant to non-anthracycline-based therapies and hormonal agents, but responds to targeted molecular therapy. Trastuzumab, an antibody against HER2, has proven effective as single agent therapy in women with HER2 overexpressed metastatic breast cancer. Moreover, in combination with chemotherapy, trastuzumab has been shown to delay disease progression and improve overall survival for women with HER2-positive advanced breast cancer. The combination of chemotherapy and trastuzumab is emerging as a standard of care in women with HER2 overexpressed metastatic breast cancer. Several combination regimens using trastuzumab with taxanes, vinca alkaloids, or platinum compounds have demonstrated efficacy in first- and second-line treatment settings. However, the development of anthracycline-based combinations has been limited by concerns of related cardiotoxicity. Newer multi-agent regimens are in development. The optimal combination, duration, and sequence of trastuzumab therapy remain unknown in patients with HER2-positive metastatic disease. The role of continuing treatment after disease progression is also unclear. Evidence from some retrospective analyses suggest HER2-positive tumors are relatively resistant to tamoxifen and perhaps more responsive to aromatase inhibitors, although such data are inconclusive. HER2 status should not be used routinely for clinical decision making regarding hormonal therapy options. Several ongoing trials are attempting to address these and other issues related to HER2 testing to select the most appropriate candidates for these emerging therapies. While many questions remain, the treatment of HER2 overexpressing metastatic breast cancer is rapidly evolving, and represents a new approach to treatment in oncology.

Treatment of breast cancer during pregnancy

The management of breast cancer during pregnancy is one of the great clinical challenges in oncology. Patients are best served by care provided through a multidisciplinary team including surgeons, oncologists, obstetricians and genetics counsellors with experience in caring for similar women. The risks of diagnostic and therapeutic interventions can be mitigated by the consideration of known side effects of therapy on the fetus and the mother. However, because of the limited amount of clinical experience available, the potential risks to the patient, to the fetus and to the pregnancy are difficult to quantify. Treatment decisions need to be tailored carefully to the individual, respecting both her clinical circumstances and her personal preferences.

New combinations with Herceptin in metastatic breast cancer

Preclinical data indicate that trastuzumab (Herceptin) has the potential for synergistic or additive effects in combination with therapies including chemotherapy and hormonal agents, providing the rationale for a number of clinical trials in women with HER2-positive metastatic breast cancer. A recently reported phase II trial has demonstrated that trastuzumab plus vinorelbine is both effective (overall response rate 75%) and well tolerated, with the major side effects being typical of single-agent vinorelbine. Other combinations of trastuzumab with a variety of other chemotherapeutic and hormonal agents are also being assessed. In an effort to overcome the cardiotoxicity observed with trastuzumab plus doxorubicin in the pivotal phase III trial, combination regimens involving potentially less toxic anthracyclines such as epirubicin and liposomal formulations of doxorubicin are ongoing. In addition, trials are investigating whether trastuzumab can reverse the resistance to hormonal therapy that develops in most women with metastatic breast cancer. These and other studies will identify the regimens that produce the best outcomes with the fewest possible side effects in women with HER2-positive breast cancer.

New cytotoxic agents and schedules for advanced breast cancer

Cytotoxic chemotherapy is important for treatment of women with hormone-insensitive or hormone-refractory advanced breast cancer. A variety of agents are effective, alone or in combination. The clinical activity and side effects of many agents, as well as principles for use of chemotherapy, are reviewed. Recent advances in chemotherapy for breast cancer include important studies on the role of dose-intensity, modifications of available agents to reduce side effects, and the availability of oral chemotherapeutics. Finally, the combination of chemotherapy with novel biological agents may improve outcomes for women with certain types of breast cancer. The growing availability of such biological therapies given in combination with chemotherapy may mean better survival in the future for women with advanced breast cancer.

Clinical Activity of Trastuzumab and Vinorelbine in Women With HER2-Overexpressing Metastatic Breast Cancer

PURPOSE: To determine the response rate and toxicity profile of trastuzumab administered concurrently with weekly vinorelbine in women with HER2-overexpressing advanced breast cancer.

PATIENTS AND METHODS: Forty women with HER2-positive (+3 by immunohistochemistry, n = 30; +2 or positive, n = 10) breast cancer were enrolled onto a study of trastuzumab (4 mg/kg × 1, 2 mg/kg weekly thereafter) and vinorelbine (25 mg/m2 weekly, with dose adjusted each week for neutrophil count). Eighty-two percent of women had received prior chemotherapy as part of adjuvant (30%), metastatic (25%), or both (28%) treatment, including substantial portions of patients who had previously received either anthracyclines (20%), taxanes (15%), or both types (38%) of chemotherapy.

RESULTS: Responses were observed in 30 of 40 patients (overall response rate, 75%, conditional corrected 95% confidence interval, 57% to 89%). The response rate was 84% in patients treated with trastuzumab and vinorelbine as first-line therapy for metastatic disease, and 80% among HER2 +3 positive patients. High response rates were also seen in women treated with second- or third-line therapy, and among patients previously treated with anthracyclines and/or taxanes. Combination therapy was feasible; patients received concurrent trastuzumab and vinorelbine in 93% of treatment weeks. Neutropenia was the only grade 4 toxicity. No patients had symptomatic heart failure. Grade 2 cardiac toxicity was observed in three patients. Prior cumulative doxorubicin dose in excess of 240 mg/m2 and borderline pre-existing cardiac function were associated with grade 2 cardiac toxicity.

CONCLUSION: Trastuzumab in combination with vinorelbine is highly active in women with HER2-overexpressing advanced breast cancer and is well tolerated.

Docetaxel administered on a weekly basis for metastatic breast cancer

PURPOSE

To evaluate the safety and efficacy of weekly docetaxel in women with metastatic breast cancer.

PATIENTS AND METHODS

Twenty-nine women were enrolled onto a study of weekly docetaxel given at 40 mg/m(2)/wk. Each cycle consisted of 6 weeks of therapy followed by a 2-week treatment break, repeated until disease progression or removal from study for toxicity or patient preference. Fifty-two percent of patients had been previously treated with adjuvant chemotherapy; 21% had received prior chemotherapy for metastatic breast cancer, and 31% had previously received anthracyclines. All patients were assessable for toxicity; two patients were not assessable for response but are included in an intent-to-treat analysis.

RESULTS

Patients received a median of 18 infusions, with a median cumulative docetaxel dose of 720 mg/m(2). There were no complete responses. Twelve patients had partial responses (overall response rate, 41%; 95% confidence interval, 24% to 61%), all occurring within the first two cycles. Similar response rates were observed among subgroups of patients previously treated either with any prior chemotherapy or with anthracyclines. An additional 17% of patients had stable disease for at least 6 months. The regimen was generally well tolerated. There was no grade 4 toxicity. Only 28% of patients had any grade 3 toxicity, most commonly neutropenia and fatigue. Acute toxicity, including myelosuppression, was mild. Fatigue, fluid retention, and eye tearing/conjunctivitis became more common with repetitive dosing, although these side effects rarely exceeded grade 2. Dose reductions were made for eight of 29 patients, most often because of fatigue (n = 5).

CONCLUSION

Weekly docetaxel is active in treating patients with metastatic breast cancer, with a side effect profile that differs from every-3-weeks therapy.

Phase I study of Doxil and vinorelbine in metastatic breast cancer

BACKGROUND

Vinorelbine and Doxil (liposomal doxorubicin) are active chemotherapeutic agents in metastatic breast cancer. A phase I study was designed to evaluate combination therapy.

PATIENTS AND METHODS

Thirty women with metastatic breast cancer were enrolled. Dose-limiting toxicity was determined through a dose escalation scheme, and defined for the first treatment cycle, only. Pharmacokinetic studies were performed during the first cycle of treatment.

RESULTS

In the first cohort of Doxil 30 mg/m2 day 1 and vinorelbine 25 mg/m2 days 1 and 8, patients experienced severe neutropenia. Vinorelbine administration was changed thereafter to days 1 and 15 of each cycle. Dose limiting toxicity was observed at Doxil 50 mg/m2 and vinorelbine 25 mg/m2. Doxil 40 mg/m2 and vinorelbine 30 mg/m2 was defined as the maximally tolerated dose. Few toxicities (principally neutro penia) were seen at this dose level, with the notable absence of significant nausea, vomiting, or alopecia. Though 63% of patients had received prior anthracycline-based chemotherapy, only one patient developed grade 2 cardiac toxicity. Pharmacokinetic studies revealed prolonged exposure to high doxorubicin concentrations for several days following Doxil administration.

CONCLUSIONS

Combination chemotherapy with Doxil and vinorelbine affords treatment with two active drugs in women with metastatic breast cancer, and appears to have a favorable toxicity profile. A schedule of Doxil 40 mg/m2 day 1 and vinorelbine 30 mg/m2 days 1 and 15 given every 28 days is recommended for phase II studies.

Use of alternative medicine by women with early-stage breast cancer

BACKGROUND

We analyzed the use of alternative medicine by women who had received standard therapy for early-stage breast cancer diagnosed between September 1993 and September 1995.

METHODS

A cohort of 480 patients with newly diagnosed early-stage breast cancer was recruited from a Massachusetts statewide cohort of women participating in a study of how women choose treatment for cancer. Alternative medical treatments, conventional therapies, and health-related quality of life were examined.

RESULTS

New use of alternative medicine after surgery for breast cancer was common (reported by 28.1 percent of the women); such use was not associated with choices about standard medical therapies after we controlled for clinical and sociodemographic variables. A total of 10.6 percent of the women had used alternative medicine before they were given a diagnosis of breast cancer. Women who initiated the use of alternative medicine after surgery reported a worse quality of life than women who never used alternative medicine. Mental health scores were similar at base line among women who decided to use alternative medicine and those who did not, but three months after surgery the use of alternative medicine was independently associated with depression, fear of recurrence of cancer, lower scores for mental health and sexual satisfaction, and more physical symptoms as well as symptoms of greater intensity. All groups of women reported improving quality of life one year after surgery.

CONCLUSIONS

Among women with newly diagnosed early-stage breast cancer who had been treated with standard therapies, new use of alternative medicine was a marker of greater psychosocial distress and worse quality of life.

Determinants of helper T cell-dependent antibody production

Multiple factors regulate the development and maintenance of humoral immune responses. The cytokines produced by helper T cells are major determinants of the magnitude and phenotype of antibody responses to protein antigens. Th2-derived cytokines are most effective at initiating primary B cell responses, whereas Th1 cells are effective helpers for B cells exposed to multivalent antigens and for previously activated B cells. In addition, different cytokines stimulate B cell switching to particular antibody isotypes. Cytokine production can be regulated in vivo by the conditions of antigen exposure, and by the nature of antigens. Tolerogenic antigens alter the phenotypes of antibody responses by preferentially inactivating selected subsets of helper T cells. Morphologic techniques provide potentially valuable approaches for studying T/B cell interactions and the nature and consequences of local cytokine production in situ, in lymphoid tissues.

In vivo role of interleukin 4 in T cell tolerance induced by aqueous protein antigen

High doses of aqueous protein antigens induce a form of immunological tolerance in which interleukin 2 (IL-2)- and interferon gamma (IFN-gamma)-secreting T helper type 1 (Th1) cells are inhibited, but IL-4-secreting (Th2) cells are not. This is manifested by reduced proliferation of antigen-specific T cells upon in vitro restimulation, and marked suppression of specific antibody responses of the immunoglobulin (Ig)G2a, IgG2b, and IgG3 isotypes, but not of IgG1 and IgE. The role of the immunomodulatory cytokine IL-4 in this model of unresponsiveness to protein antigens has been examined. Administration of tolerizing antigen itself primes splenic CD4+ T cells for secretion of lymphokines, both IL-2 and IL-4. Neutralization of IL-4 in vivo with the anti-IL-4 antibody 11B11 during tolerance induction augments IFN-gamma production by T cells of tolerant mice, and reverses the suppression of IgG2a, IgG2b, and IgG3. This blockade of IL-4 function does not, however, restore the proliferative responses of T cells, suggesting that reduced T cell proliferation is due to direct T cell inactivation or anergy. Inhibiting the activity of IL-4 in vivo also inhibits the expansion of antigen-specific Th2-like cells, which are resistant to the induction of unresponsiveness. Thus, the immunologic consequences of high-dose tolerance are due to a combination of clonal T cell anergy and IL-4-mediated immune regulation.

Aqueous antigens induce in vivo tolerance selectively in IL-2- and IFN-gamma-producing (Th1) cells

As a model for understanding in vivo immune responses, we have exposed mice to aqueous haptenated-protein Ag, and examined immune responses to subsequent immunization with Ag in adjuvant. Pretreating mice with soluble, TNP-conjugated Ag induces selective nonresponsiveness to Ag for both humoral and cell-mediated immune functions. Specific T cell proliferation in response to Ag is inhibited, and Ag-induced secretion of the lymphokines IL-2 and IFN-gamma, but not IL-4, is reduced. B cell responses after pretreatment are also affected. Although levels of TNP-specific IgG1 and IgE are similar in treated and untreated mice, soluble Ag pretreatment diminishes production of TNP-specific IgG2a and IgG2b. This is due to lack of T cell help and is not caused by tolerance in the B cell compartment. These results indicate that pretreatment of mice with aqueous Ag induces selective unresponsiveness in Th1-like Th cells, which secrete IL-2 and IFN-gamma, but not in Th2-like Th cells, which secrete IL-4.

Aqueous antigens induce in vivo tolerance selectively in IL-2- and IFN-gamma-producing (Th1) cells

As a model for understanding in vivo immune responses, we have exposed mice to aqueous haptenated-protein Ag, and examined immune responses to subsequent immunization with Ag in adjuvant. Pretreating mice with soluble, TNP-conjugated Ag induces selective nonresponsiveness to Ag for both humoral and cell-mediated immune functions. Specific T cell proliferation in response to Ag is inhibited, and Ag-induced secretion of the lymphokines IL-2 and IFN-gamma, but not IL-4, is reduced. B cell responses after pretreatment are also affected. Although levels of TNP-specific IgG1 and IgE are similar in treated and untreated mice, soluble Ag pretreatment diminishes production of TNP-specific IgG2a and IgG2b. This is due to lack of T cell help and is not caused by tolerance in the B cell compartment. These results indicate that pretreatment of mice with aqueous Ag induces selective unresponsiveness in Th1-like Th cells, which secrete IL-2 and IFN-gamma, but not in Th2-like Th cells, which secrete IL-4.

Humoral immune functions in IL-4 transgenic mice

We have analyzed mice expressing IL-4 as a transgene, and found that expression of this lymphokine has profound effects on B cell function. B cells from transgenic mice exhibit phenotypic changes, including an increase in size and elevated expression of class II MHC. IL-4 increases the quantity of IgE produced by transgenic-derived B cells in response to LPS stimulation. In vivo, IL-4 markedly affects the serum Ig isotype repertoire. Serum levels of IgG1 and IgE are elevated, and levels of IgG2a, IgG2b, and IgG3 are depressed in IL-4 transgenic mice. Ag-specific antibody responses to immunization with hapten-carrier conjugates are also affected by IL-4. Transgenic mice show increased anti-hapten IgE and IgG1 and reduced anti-hapten IgG2a, IgG2b, and IgG3, compared with wild-type mice. Ag-specific IgE is substantially induced by T cell-dependent Ag, but not T cell-independent Ag, suggesting that cognate T-B interactions in addition to IL-4 are required for generating IgE responses in vivo. In vivo treatment with the anti-IL-4 mAb 11B11 reverses many of the isotype alterations in the transgenic mice, indicating that these changes arise as a direct consequence of IL-4 secretion.

Humoral immune functions in IL-4 transgenic mice

We have analyzed mice expressing IL-4 as a transgene, and found that expression of this lymphokine has profound effects on B cell function. B cells from transgenic mice exhibit phenotypic changes, including an increase in size and elevated expression of class II MHC. IL-4 increases the quantity of IgE produced by transgenic-derived B cells in response to LPS stimulation. In vivo, IL-4 markedly affects the serum Ig isotype repertoire. Serum levels of IgG1 and IgE are elevated, and levels of IgG2a, IgG2b, and IgG3 are depressed in IL-4 transgenic mice. Ag-specific antibody responses to immunization with hapten-carrier conjugates are also affected by IL-4. Transgenic mice show increased anti-hapten IgE and IgG1 and reduced anti-hapten IgG2a, IgG2b, and IgG3, compared with wild-type mice. Ag-specific IgE is substantially induced by T cell-dependent Ag, but not T cell-independent Ag, suggesting that cognate T-B interactions in addition to IL-4 are required for generating IgE responses in vivo. In vivo treatment with the anti-IL-4 mAb 11B11 reverses many of the isotype alterations in the transgenic mice, indicating that these changes arise as a direct consequence of IL-4 secretion.

T-cell-mediated activation of B cells

Antibody responses to protein antigens are dependent on helper T lymphocytes, which provide necessary growth and differentiation, inducing stimuli to antigen-specific B cells. Recent investigations have focused on the mechanisms of T-B interactions, and the nature of the T-cell-derived signals that are needed for activation and expansion of B cells.

Functional phospholipid/sphingomyelin ratio: an easy to interpret indicator of fetal lung maturity

Data are presented which show that the functional phospholipid/sphingomyelin (FPL/S) ratio is a sensitive and specific prenatal indicator of fetal respiratory status. Phospholipids included in the ratio are acetone precipitable lecithin(L), phosphatidylglycerol(PG), phosphatidylethanolamine(PE), and sphingomyelin(S). These lipids have been shown to contribute to either the lowering of surface tension or to changes in microviscosity. Both of these properties contribute independently to the physiologic effectiveness of fetal lung surfactant. Although other phospholipid profiles have been described in the literature, the FPL/S ratio accounts for the major phospholipids which contribute to lung surfactant function with the added advantage of presenting the data in the form of a single easy to interpret number. Clinical correlates are also presented for the L/S ratio, fluorescence polarization assay (using 1,6-diphenyl-3,5-hexatriene), and absorbance at 650 nanometers.

Degree of unsaturation of the fatty acid chains of phospholipids influences the fluorescence polarization: implications for evaluating fetal lung maturity

To study the effect of fatty acid chain saturation on the fluorescence polarization assay as a measure of fetal lung maturity, we used purified phospholipids isolated from human amniotic fluid and various commercial phospholipids. We found that the fluorescence polarization value decreased as the concentration of unsaturated fatty acids increased. In contrast, the lecithin/sphingomyelin ratio increases with increasing amounts of saturated lecithin, produced as the fetal lung matures. Since only saturated lecithins are surface active, the two indices of fetal respiratory status must reflect different properties of lung surfactant.

Degree of unsaturation of the fatty acid chains of phospholipids influences the fluorescence polarization: implications for evaluating fetal lung maturity

To study the effect of fatty acid chain saturation on the fluorescence polarization assay as a measure of fetal lung maturity, we used purified phospholipids isolated from human amniotic fluid and various commercial phospholipids. We found that the fluorescence polarization value decreased as the concentration of unsaturated fatty acids increased. In contrast, the lecithin/sphingomyelin ratio increases with increasing amounts of saturated lecithin, produced as the fetal lung matures. Since only saturated lecithins are surface active, the two indices of fetal respiratory status must reflect different properties of lung surfactant.