Determining the association of insurance coverage and survival outcomes in patients with olfactory neuroblastoma utilizing machine learning

KEY POINTS

We use machine learning to examine health insurance and mortality in olfactory neuroblastoma. Private insurance significantly improved survival even after adjusting for confounders. The regression model also found no statistical difference between Medicare and no insurance.

Imbrication of Anterior Digastric with Advancement of the Posterior Digastric and Its Implications in Neck Aesthetics

Background: To describe a novel technique to modify the proportional length of the anterior-to-posterior digastric muscles to improve neck aesthetics. Objective: To provide an objective measure to quantify neck rejuvenation and a novel technique to adjust the digastric ratio. Design: We retrospectively compared 52 patients who had neck rejuvenation with or without digastric manipulation. Preoperative and postoperative images were analyzed and compared with computer software using a novel analysis technique to measure the digastric ratio and neck height. Distances between the menton, cervical point (CP), and gonion were measured. Results: The anterior-to-posterior digastric ratio improved an average of 26.5% (p < 0.01) in the new technique group, 15.9% in the control group. Distance of the CP to the inferior edge of the mandible decreased an average of 13.9% using the new technique. Conclusion: The ratio of anterior-to-posterior digastric muscle appears to improve as well as the neck height with manipulation of the digastric muscles.

Microbial Changes Associated With Oral Cavity Cancer Progression

OBJECTIVE

To examine the oral microbiome in the context of oral cavity squamous cell carcinoma.

STUDY DESIGN

Basic science research.

SETTING

Academic medical center.

METHODS

Oral swabs were collected from patients presenting to the operating room for management of oral cavity squamous cell carcinoma and from age- and sex-matched control patients receiving surgery for unrelated benign conditions. 16S ribosomal RNA (rRNA) sequencing was performed on genetic material obtained from swabs. A bacterial rRNA gene library was created and sequence reads were sorted into taxonomic units.

RESULTS

Thirty-one control patients (17 males) and 35 cancer patients (21 males) were enrolled. Ages ranged from 23 to 89 (median 63) for control patients and 35 to 86 (median 66) for cancer patients. Sixty-one percent of control patients and 63% of cancer patients were smokers. 16S analyses demonstrated a significant decrease in Streptococcus genera in oral cancer patients (34.11% vs 21.74% of the population, p = .04). Increases in Fusobacterium, Peptostreptococcus, Parvimonas, and Neisseria were also found. The abundance of these bacteria correlated with tumor T-stage.

CONCLUSION

16S rRNA sequencing demonstrated changes in bacterial populations in oral cavity cancer and its progression compared to noncancer controls. We found increases in bacteria genera that correspond with tumor stage-Fusobacteria, Peptostreptococcus, Parvimonas, Neisseria, and Treponema. These data suggest that oral cancer creates an environment to facilitate foreign bacterial growth, rather than implicating a specific bacterial species in carcinogenesis. These bacteria can be employed as a potential marker for tumor progression or interrogated to better characterize the tumor microenvironment.

Right Vocal Cord Paralysis Caused by Histoplasmosis: A Case Report

OBJECTIVES

Histoplasma capsulatum is a prevalent dimorphic fungus, reaching an exposure rate of 90% in endemic areas such as the Midwest and Central United States. We report an unusual presentation of dysphonia due to right vocal cord paralysis caused by mediastinal lymphadenopathy from histoplasmosis.

METHODS

A 73-year-old male presented to an otolaryngology clinic with 4 months of hoarseness. Flexible strobolaryngoscopy demonstrated right vocal cord paralysis in lateral position and a full length glottic gap. Computerized tomography (CT) scan showed enlargement of a right paratracheal node.

RESULTS

A lymph node biopsy was obtained and showed histoplasmosis. He was treated with a 3-month course of pozaconazole. He then received a vocal cord medialization injection 2 months after symptom onset, which produced favorable improvement of his symptoms at 8-month follow up.

CONCLUSIONS

One other case report in the literature has reported left vocal cord paralysis related to histoplasmosis. This first case of right vocal cord paralysis was extremely unusual and is not often included in the differential diagnosis of vocal cord paralysis.

Recommendations for Care of Survivors of Head and Neck Cancer

This JAMA Clinical Guidelines Synopsis summarizes the American Head and Neck Society’s 2021 consensus statement on care of survivors of head and neck cancer.

Development and Validation of a Decision Analytical Model for Posttreatment Surveillance for Patients With Oropharyngeal Carcinoma

IMPORTANCE

Clinical practice regarding posttreatment radiologic surveillance for patients with oropharyngeal carcinoma (OPC) is neither adapted to individual patient risk nor fully evidence based.

OBJECTIVES

To construct a microsimulation model for posttreatment OPC progression and use it to optimize surveillance strategies while accounting for both tumor stage and human papillomavirus (HPV) status.

DESIGN, SETTING, AND PARTICIPANTS

In this decision analytical modeling study, a Markov model of 3-year posttreatment patient trajectories was created. The training data source was the American College of Surgeon's National Cancer Database from 2010 to 2015. The external validation data set was the 2016 International Collaboration on Oropharyngeal Cancer Network for Staging (ICON-S) study. Training data comprised 2159 patients with OPC treated with primary radiotherapy who had known HPV status and disease staging information. Patients with American Joint Committee on Cancer, 7th edition stage III to IVB disease and those with clinical metastases during the time of primary treatment were included. Data were analyzed from August 1 to October 31, 2020.

MAIN OUTCOMES AND MEASURES

Main outcomes included disease stage and HPV status, specific disease transition probabilities, and latency of surveillance regimens, defined as time between recurrence incidence and disease discovery.

RESULTS

Training data consisted of 2159 total patients (1708 men [79.1%]; median age, 59.6 years [range, 40-90 years]; 401 with stage III disease, 1415 with stage IVA disease, and 343 with stage IVB disease). Cohorts predominantly had HPV-negative disease (1606 [74.4%]). With model-optimized regimens, recurrent disease was discovered a mean of 0.6 months (95% CI, 0.5-0.8 months) earlier than with a standard surveillance regimen based on current clinical guidelines. Recurrent disease was discovered using the optimized regimens without significant reduction in sensitivity. Compared with strategies based on reimbursement guidelines, the model-optimized regimens found disease a mean of 1.8 months (95% CI, 1.3-2.3 months) earlier.

CONCLUSIONS AND RELEVANCE

Optimized, risk-stratified surveillance regimens consistently outperformed nonoptimized strategies. These gains were obtained without requiring any additional imaging studies. This approach to risk-stratified surveillance optimization is generalizable to a broad range of tumor types and risk factors.

Mathematical predication models to optimize post-treatment surveillance in HPV-associated oropharyngeal cancer

6027

Background: In this study we develop post-treatment imaging surveillance schedules for locally advanced oropharyngeal carcinoma (OPC) specific to the unique recurrence patterns of tumor stage and HPV status, using mathematical models. Current post-treatment imaging surveillance recommendations for OPC are not evidence based. The exception is the use of a positron emission tomography (PET) scan at 3 months post-treatment, after which practice across institutions diverge. An optimized and personalized surveillance schedule for OPC patients can minimize costs and diagnostic delays. Methods: A Markov multi-state model defining local and distant recurrences was trained using 2159 patients from the National Cancer Database. Patients from 2010-2015 treated at an academic or major cancer center with curative radiotherapy were included. Tumors must have been stage III to IVB (AJCC 7th edition) with known p16/HPV status. Model performance was then successfully externally validated using the 2016 International Collaboration on Oropharyngeal cancer Network for Staging (ICON-S) study. Optimized radiographic surveillance schedules were created using this model, assuming a PET at month 3 and including 0 to 6 additional computed tomography (CT) scans of the neck and chest. Optimization was done for minimization of latency, defined as time between disease recurrence and radiographic discovery. Results: Model-selected schedules varied significantly from commonly utilized-surveillance schedules (such as imaging every 3 months within the first year from treatment) and showed lower mean diagnostic latency for every stage and HPV status (shown in Table). In the lowest risk cohort (Stage III HPV+), the optimized schedule had a sensitivity of 65% and latency of 3.1 months. In the highest risk group (Stage IVB HPV-), the optimized schedule had a sensitivity of 76% and latency of 1.9 months. Conclusions: Mathematical model optimization for HPV status and stage is feasible and produces non-intuitive results. These results could be used to inform surveillance if payors reimburse for fewer total scans. Across all cohorts, each added CT scan increases surveillance sensitivity and decreases latency. Incorporation of physical exam and direct visualization results into the model are still needed. Future steps include cost effectiveness research and prospective clinical trials.[Table: see text]

The PatB protein of Bacillus subtilis is a C-S-lyase

The PatB protein of Bacillus subtilis had both cystathionine beta-lyase and cysteine desulfhydrase activities in vitro. The apparent K(m) value of the PatB protein for cystathionine was threefold higher than that of the MetC protein, the previously characterized cystathionine beta-lyase of B. subtilis. In the presence of cystathionine as sole sulfur source, the patB gene present on a multicopy plasmid restored the growth of a metC mutant. In addition, the patB metC double mutant was unable to grow in the presence of sulfate or cystine while the patB or metC single mutants grew similarly to the wild-type strains in the presence of the same sulfur sources. In a metC mutant, the PatB protein can replace the MetC enzyme in the methionine biosynthetic pathway.

Regional differences in waiting time to pregnancy among fertile couples from four European cities

BACKGROUND

A previous European study found a longer time to pregnancy (TTP) among fertile women from Paris compared with women from other Western European countries. A co-ordinated, cross-sectional study of pregnant couples from Denmark (Copenhagen), France (Paris), Scotland (Edinburgh) and Finland (Turku) was therefore undertaken to assess differences in waiting TTP among couples from these cities.

METHODS

Pregnant women were invited to participate when they showed up for their first antenatal visit in one of the four centres. Inclusion criteria included that their partner was 20-45 years of age and born in the country in which he was currently living and that the pregnancy was achieved without fertility treatment. Both partners filled in a questionnaire and the man underwent a physical examination and delivered a semen sample (Turku: n = 237, Copenhagen: n = 302, Edinburgh: n = 212, Paris: n = 191).

RESULTS

French couples had a decreased probability of conception compared with couples from the other three countries, although only after adjustment for confounders. No significant differences between couples from the three other countries were found.

CONCLUSION

The observed geographical differences in TTP remain unexplained and were not due to differences in semen quality, but may be caused by varying exposures to environmental factors or psychological distress. In addition, selection bias due to the low participation rates cannot be ruled out. Future studies examining the causes for geographical differences in TTP are needed.

Stavudine plus didanosine and nevirapine in antiretroviral-naive HIV-infected adults: preliminary safety and efficacy results. VIRGO Study Team

The objective of this open-label trial is to evaluate the virological and immunological effects of triple therapy with stavudine (40 mg twice daily if > or = 60 kg, 30 mg twice daily if < 60 kg)/didanosine (400 mg once daily if > or = 60 kg, 300 mg once daily if < 60 kg)/nevirapine (200 mg daily from day 1 to 14, then 200 mg twice daily) in 60 antiretroviral-naive HIV-infected adults with CD4 cell counts > or = 200 cells/mm3 and plasma HIV RNA > or = 5000 copies/ml. At present, 59 patients have begun receiving the trial regimen. Characteristics of patients at baseline were as follows: 46 men/13 women, CDC stage A, 75%; mean CD4 cell count, 429 cells/mm3; mean HIV RNA, 4.6 log10 copies/ml). Mean decrease of viral load was -1.9 log10 at week 4 (n = 39), -1.9 log10 at week 16 (n = 20), with HIV RNA below the detectable level (< 500 copies/ml) in 62% of patients at week 4 and 85% at week 16. Mean CD4 cell count increase was +118 cells/mm3 at week 4. Cutaneous intolerance occurred within the first 4 weeks in 11/59 (19%) patients after a mean of 14 days (range, 3-24 days) and led to nevirapine discontinuation in 3/11 patients. Preliminary results of this ongoing trial show that combination therapy with stavudine/didanosine/nevirapine is a convenient (seven pills in two daily intakes) triple-therapy regimen with rapid immunological and antiviral effects. Rash, frequent in the first weeks of therapy, usually can be managed without stopping nevirapine. Long-term suppression of plasma HIV RNA with this combination needs to be confirmed but may support use of nevirapine as a component of first-line anti-HIV therapy along with two nucleosides.

Cardiac M(2) muscarinic cholinoceptor activation by human chagasic autoantibodies: association with bradycardia

OBJECTIVE

To assess whether exposure of cardiac muscarinic acetylcholine receptors (mAChR) to activating chagasic antimyocardial immunoglobulins results in bradycardia and other dysautonomic symptoms associated with the regulation of heart rate.

METHODS

Trypanosoma cruzi infected patients with bradycardia and other abnormalities in tests of the autonomic nervous system were studied and compared with normal subjects. Antipeptide antibodies in serum were demonstrated by an enzyme linked immunosorbent assay using a synthetic 24-mer-peptide corresponding antigenically to the second extracellular loop of the human heart M(2) mAChR. The functional effect of affinity purified antipeptide IgG from chagasic patients on spontaneous beating frequency and cAMP production of isolated normal rat atria was studied.

RESULTS

There was a strong association between the finding of antipeptide antibodies in chagasic patients and the presence of basal bradycardia and an altered Valsalva manoeuvre (basal bradycardia: chi(2) = 37.5, p < 0. 00001; Valsalva manoeuvre: chi(2) = 70.0, p < 0.00001). The antipeptide autoantibodies also showed agonist activity, decreasing the rate of contraction and cAMP production. The effects on rat atria resembled the effects of the authentic agonist and those of the total polyclonal chagasic IgG, being selectively blunted by atropine and AF-DX 116, and neutralised by the synthetic peptide corresponding in amino acid sequence to the second extracellular loop of the human M(2) mAChR.

CONCLUSIONS

There is an association between circulating antipeptide autoantibodies in chagasic patients and the presence of bradycardia and other dysautonomic symptoms. Thus these autoantibodies are a marker of autoimmune cardiac autonomic dysfunction. The results support the hypothesis that autoimmune mechanisms play a role in the pathogenesis of chagasic cardioneuromyopathy.

Efficacy and safety of stavudine and didanosine combination therapy in antiretroviral-experienced patients

OBJECTIVES

To assess the efficacy, tolerance, and safety of combination antiretroviral therapy with didanosine and stavudine in HIV-infected patients with CD4+ cell counts > 100 x 10(6)/l and HIV plasma RNA > 10(4) copies/ml previously treated with other antiretroviral agents for at least 3 months.

DESIGN

In this open, multicentre, non-randomized, Phase II pilot study, adult patients were administered didanosine (200 mg twice daily) plus stavudine (40 mg twice daily) for 6 months. Patients for whom the first regimen had led to undetectable HIV RNA levels were offered a second 6-month course of treatment; those who had achieved insufficient immunological and virological gains in the first 6 months were given a new combination.

METHODS

Primary evaluation of efficacy was based on viral load measured by branched DNA second-generation testing (lower limit of detection, 500 copies/ml) and CD4+ cell counts; secondary evaluations included AIDS-defining events and clinical side-effects.

RESULTS

Sixty-five patients with median prior antiretroviral therapy of 24 months (65 with zidovudine, 29 with zalcitabine) were included in the study. At baseline, median CD4+ cell count was 198 x 10(6)/l and median plasma HIV RNA was 80000 copies/ml (4.9 log10 copies/ml). In this heavily pretreated population, an increase in the mean CD4+ cell count was observed (+70 x 10(6)/l at 24 weeks). In addition, rapid and prolonged antiviral activity was seen, with a mean maximal decrease of 1.1 log10 copies/ml at week 4, a mean decrease of 0.89 log10 copies/ml at week 24, and a plasma RNA viraemia < 500 copies/ml achieved in 14% of patients at week 24.

CONCLUSIONS

Combination therapy with stavudine and didanosine is safe and leads to a sustained antiviral effect, even in patients with prolonged prior antiretroviral exposure and low CD4+ cell counts.

C16 and C17 derivatives of estradiol as inhibitors of 17 beta-hydroxysteroid dehydrogenase type 1: chemical synthesis and structure-activity relationships

As a first part of our research focused on the synthesis of 17 beta-HSD type 1 inhibitors without estrogenic activity, we needed to identify a small, easy-to-handle pharmacophore able to block the enzymatic activity. Previous studies on the active site of the enzyme by affinity labeling gave us a basis for the design of steroidal inhibitors derivatives. Several estradiol derivatives bearing a short (three carbons) side chain in position 17 alpha or 16 alpha were synthesized and tested for their ability to inhibit the transformation of estrone into estradiol by 17 beta-HSD type 1 (cytosolic fraction of human placenta). We found that 16 alpha-derivatives of estradiol gave better 17 beta-HSD inhibition than their corresponding 17 alpha analogs. Among several chemical groups used in this study, we conclude that better 17 beta-HSD inhibition was obtained for compounds with a good leaving group at the end of side chain. Thus, an iodopropyl or a bromopropyl side chain at C16 alpha of estradiol (E2) inhibit efficiently the 17 beta-HSD type 1 with IC50 values of 0.42 and 0.46 microM, respectively. Their 17-keto analogs inhibit also the enzyme activity similarly. Since this kind of compounds inhibit the 17 beta-HSD type 1 in time-dependent manner and that enzymatic activity cannot be restored later, we conclude to inhibitor of inactivator type. This conclusion is in accordance with the correlation observed between the ability of leaving group to dissociate and their potency to inhibit 17 beta-HSD type 1. We have also observed that additional addition of untritiated estrone protect the enzyme against the inactivation caused by 16 alpha-bromopropyl-E2 suggesting a competitive inhibitor of 17 beta-HSD. The bromopropyl pharmacophore was then selected to be further added onto an antiestrogenic steroid nucleus.

A 6beta-(thiaheptanamide) derivative of estradiol as inhibitor of 17beta-hydroxysteroid dehydrogenase type 1

In an effort to develop potent agents for reducing the levels of the active estrogen, estradiol, we developed a new category of 17beta-hydroxysteroid dehydrogenase (17beta-HSD) type 1 inhibitors. The compounds described possess a butyl methyl alkylamide side chain linked to the C6 position of estradiol by a thioether. With a series of epimeric mixtures, an optimal side-chain length of five methylene groups (between the amide group and steroid part) was first determined. Thereafter, both C6 epimers of optimized mixture were obtained after high-pressure liquid chromatography separation. 1H and 13C NMR experiments were performed to confirm the stereochemistry of each epimer. The 6beta-orientation of the side-chain was found to be crucial for enzymatic inhibition. Indeed, for the optimized side-chain length, the compound with a beta-orientation (5: N-butyl,N-methyl 7-(3',17'beta-dihydroxy-1',3',5'( 10')-estratriene-6'beta-yl)-7-thiaheptanamide) was 70-fold more potent than the 6alpha-analog. Compound 5 did not inactivate 17beta-HSD type 1, suggesting a reversible inhibitor. In addition, it was found to be a more potent inhibitor than the substrate estrone itself or a panel of three known inhibitors.

Steroidal spiro-gamma-lactones that inhibit 17 beta-hydroxysteroid dehydrogenase activity in human placental microsomes

The important enzyme 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) is known to regulate intracellular levels of biologically active steroids, namely, androgens and estrogens. In an effort to develop potent inhibitors of 17 beta-HSD for reducing the levels of active steroids, we found that steroidal spiro-gamma-lactones inhibit 17 beta-HSD activity. In this report, we describe the synthesis of 11 spiro-gamma-lactone analogs containing a steroidal C-18 or C-19 nucleus and compare their relative inhibitory effects on 17 beta-HSD activity in the human placenta microsomes that catalyze the interconversion of androgens and estrogens. To void the interaction of the cytosolic 17 beta-HSD activity that is specific for the interconversion of estrone and estradiol, we used 4-androstenedione as substrate. Analysis of the inhibitory effect exerted by these analogs on microsomal 17 beta-HSD activity indicates that spiro-gamma-lactones containing the C-18 nucleus are more potent inhibitors than C-19 nucleus analogs. The best inhibition was obtained with the phenolic spiro-gamma-lactone 7 (3-hydroxy-19-nor-17 alpha-pregna-1,3,5(10)-triene 21,17-carbolactone), which has an IC50 value of 0.27 microM, and was much lower than the competitive effect of the unlabeled substrate 4-androstenedione, which has an IC50 value of 1.40 microM. Preincubation with lactone 7 did not inactivate 17 beta-HSD activity. The results thus suggest that lactone 7 is a reversible in inhibitor. Lactone 7 is selective for microsomal 17 beta-HSD activity, as no inhibition was observed for cytosolic 17 beta-HSD activity.

Synthesis and biological activities of thioether derivatives related to the antiestrogens tamoxifen and ICI 164384

The catalyzed coupling reaction of activated alcohol and mercaptan was used for the short and efficient synthesis of 14 thioether compounds. Two types of side chains, the methyl butyl alkylamide related to the pure steroidal antiestrogen ICI 164384 and the dimethylamino ethyloxy phenyl related to the clinically used nonsteroidal antiestrogen tamoxifen, were introduced by a thioether link on two types of nuclei (triphenylethane or estradiol). The new thioether derivatives were tested to assess their relative binding affinity for the estrogen receptor and their estrogenic or antiestrogenic activity in the ZR-75-1 (ER+) cell line. The results indicate that of the three types of compounds studied, only the nonsteroidal derivatives with an alkylamide side chain possess antiestrogenic activity. In the steroidal series, displacement of the alkylamide side chain from the 7 to the 6 position produced compounds with chemical characteristics similar to ICI 164384 or EM-139 but without antiestrogenic activity. In the nonsteroidal series of compounds with an aryl side chain, compounds with estrogenic activity were obtained. One compound, a nonsteroidal derivative with a methyl butyl alkylamide side chain 20, possesses a relative binding affinity for the estrogen receptor identical to EM-139 (1.1 and 1.2%, respectively) and a relatively good antiestrogenic activity that is 10-fold lower than EM-139 (IC50 values of 250 and 25 nM, respectively). This nonsteroidal thioether with an alkylamide side chain is free of estrogenic activity.

Synthesis of 16-(bromoalkyl)-estradiols having inhibitory effect on human placental estradiol 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD type 1)

The activity of 17 beta-HSD type 1, the enzyme that converts estrone into its more potent metabolite estradiol, has been demonstrated in all classical steroidogenic tissues and almost all peripheral tissues from both rat and human. Since 17 beta-HSD is one of the most important enzymes involved in active steroid hormone formation, its inactivation could be a clinical approach to the treatment of hormono-dependent diseases like breast cancer. Herein we report the synthesis of 16-(bromoalkyl)-estradiols and their potency to inhibit the human placenta cytosolic estradiol 17 beta-HSD (type 1). Synthetic analogues possess various side chain lengths and orientation (alpha or beta) at position 16 of the steroidal D ring. The most potent inhibitory effect was observed when the length of the side chain was 3 or 4 carbons. However, the 16 beta-(bromopropyl)-estradiol easily undergoes cyclization and its effect on 17 beta-HSD is lost. Consequently, 16 alpha-(bromopropyl)-E2, 16 alpha-(bromobutyl)-E2, and 16 beta-(bromobutyl)-E2 were the best inhibitors discussed in this paper.

Synthesis and antiestrogenic activity of diaryl thioether derivatives

The reaction of 1,2-diarylethanol and mercapto side chain catalyzed by ZnI2 was used as a key step in the short (three to five steps) and efficient synthesis of 17 diaryl thioether derivatives. Several of these compounds contain a methyl butyl amide chain and an hydroxyaryl moiety, respectively, for antiestrogenic activity and binding affinity on estrogen receptor. No binding affinity for crude cytosolic preparation of the estrogen receptor was observed for compounds without phenolic group, while a low affinity (0.01-0.05%) was measured for mono- or diphenol derivatives. Like the pure steroidal antiestrogen EM-139, these novel nonsteroidal compounds did not exert any stimulatory effect on cell proliferation of (ER+) ZR-75-1 human breast cancer cells and partially reversed the amplitude of the stimulatory effect induced by estradiol on this (ER+) cell line. No proliferative or antiproliferative effect on (ER-) MDA-MB-231 human breast cancer cells was also observed for three of these compounds (39-41). Among the newly synthesized nonsteroidal compounds, the thioether derivative 41 (N-butyl-N-methyl-13,14-bis(4'-hydroxyphenyl)-12-thiatetradecanamide+ ++), with a long methylbutylalkanamide side chain and a diphenolic nucleus, was selected as the best antiestrogenic compound. However, this compound was 100-fold less antiestrogenic in (ER+) ZR-75-1 cells than the steroidal antiestrogen EM-139.

Sequence complexities of the poly(A)-containing mRNA in uninfected soybean root and the nodule tissue developed due to the infection by Rhizobium

In order to determine the number of structural genes expressed specifically in root nodules, the total complexities of poly(A) + polysomal RNA populations from uninfected roots and mature nodules were compared. Hybridization kinetics of nodule poly(A) + RNA (NRNA) to its cDNA (NcDNA) revealed a very abundant component comprising 18--20% of the NRNA. This component was shown to be leghaemoglobin (Lb) by the similarity of its kinetics of hybridization to that of purified Lb-cDNA. The hybridization kinetics of uninfected root cDNA (RcDNA) to root poly(A) + RNA (RRNA) indicate that this abundant RNA fraction is absent in RRNA. The extent of sequence homologies between root and nodule tissue was determined by heterologous hybridizations of RcDNA to NRNA and vice versa. The data suggest that the mRNA populations of the two tissues are substantially homologous, though shifts in abundance of certain sequences are quite marked. The hybridization of purified Lb-cDNA to total polysomal RNA from developing nodules shows that the increase in concentration of Lb-mRNA sequences parallels the leghaemoglobin synthesis in this tissue. Lb sequences appear to increase between 8 and 13 days after infection with Rhizobium.