Common Invasive Fungal Pathogens in Cancer Patients: Introduction, List, Risk factors, and Keynotes

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Introduction

Common invasive fungal pathogens that frequently affect cancer patients, especially those who are immunocompromised due to chemotherapy, hematologic malignancies, or bone marrow/stem cell transplants.

List of Common Invasive Fungal Pathogens

1. Candida species

  • Candida albicans (most common)
  • Candida glabrata
  • Candida tropicalis
  • Candida parapsilosis
  • Candida krusei

Causes: Candidemia, disseminated candidiasis
Risk: Neutropenia, central venous catheter, broad-spectrum antibiotics

2. Aspergillus species

  • Aspergillus fumigatus (most frequent)
  • Aspergillus flavus
  • Aspergillus niger
  • Aspergillus terreus
  • Aspergillus lentulus

Causes: Invasive pulmonary aspergillosis (IPA), sinusitis, disseminated infection
Risk: Prolonged neutropenia, corticosteroids, hematologic malignancy

3. Mucorales (Zygomycetes)

  • Rhizopus, Mucor, Lichtheimia, Rhizomucor species

Causes: Rhinocerebral, pulmonary, or disseminated mucormycosis
Risk: Hematologic malignancy, diabetes, iron overload, voriconazole use

4. Fusarium species

Causes: Skin lesions, fungemia, pneumonia
Risk: Profound neutropenia, acute leukemia, HSCT

5. Scedosporium species

  • Scedosporium apiospermum, Lomentospora prolificans

Causes: Pulmonary, brain abscess, disseminated infections
Risk: Immunosuppression, organ transplant

6. Cryptococcus neoformans / gattii

Causes: Meningitis, pulmonary or disseminated cryptococcosis
Risk: AIDS, corticosteroid therapy, hematologic malignancy

7. Pneumocystis jirovecii

Causes: Pneumocystis pneumonia (PCP)
Risk: T-cell dysfunction, high-dose steroids, lymphoma, transplant patients

8. Talaromyces marneffei (in endemic areas like Southeast Asia)

Causes: Disseminated talaromycosis
Risk: HIV/AIDS, solid organ or hematologic malignancies

Risk Factors of Common Invasive Fungal Pathogens in Cancer Patients

Key Risk Factors in Cancer Patients:

  • Neutropenia (ANC <500/mm³)
  • Prolonged corticosteroid therapy
  • HSCT or solid organ transplant
  • Broad-spectrum antibiotics
  • Mucosal damage (e.g., mucositis)

Keynotes

  • Cancer patients are at high risk due to immunosuppression, mucosal injury, and indwelling devices.
  • Timely diagnosis is crucial; delayed treatment worsens outcomes.
  • Empiric antifungal therapy is often started in febrile neutropenic patients.
  • Species identification and susceptibility testing are crucial due to the emergence of resistance patterns.

1. Candida species

  • The most common cause of fungemia in cancer patients.
  • Species include: Candida albicans, C. glabrata, C. tropicalis, C. parapsilosis, C. krusei.
  • Risk factors: Neutropenia, central venous catheters, broad-spectrum antibiotics, mucositis.
  • Clinical forms: Candidemia, hepatosplenic candidiasis, endophthalmitis.
  • Resistance: C. glabrata shows reduced azole susceptibility.

2. Aspergillus species

  • Aspergillus fumigatus is the leading mold in immunocompromised hosts.
  • Causes: Invasive pulmonary aspergillosis (IPA), sinusitis, cerebral aspergillosis.
  • Risk factors: Prolonged neutropenia, HSCT, steroids.
  • Diagnosis: Galactomannan assay, CT scan (halo sign), fungal culture, PCR.
  • Voriconazole is the first-line treatment; A. terreus is resistant to amphotericin B.

3. Cryptococcus neoformans / gattii

  • Causes meningoencephalitis, especially in AIDS and cancer patients.
  • Encapsulated yeast, as seen in the India ink or CrAg test, is positive.
  • Inhalation route: disseminates to the CNS.
  • Risk: T-cell suppression, hematologic malignancy.
  • Treatment: Amphotericin B + flucytosine, followed by fluconazole.

4. Mucorales (Mucormycosis)

  • Agents: Rhizopus, Mucor, Lichtheimia.
  • Rapidly progressive and angioinvasive mold.
  • Forms: Rhinocerebral, pulmonary, GI, disseminated.
  • Risk: Uncontrolled diabetes, iron overload, and voriconazole prophylaxis.
  • Amphotericin B is the treatment of choice; surgical debridement is often required.

5. Fusarium species

  • Common in profound neutropenia and leukemia.
  • Causes: Skin lesions, disseminated fungemia, pneumonia.
  • Blood cultures are often positive, unlike aspergillosis.
  • High resistance to antifungals; voriconazole/liposomal amphotericin B used.

6. Scedosporium / Lomentospora

  • Found in soil; causes infection in immunocompromised patients.
  • May mimic Aspergillus but is resistant to amphotericin B.
  • Often disseminated; CNS involvement is common.
  • Voriconazole is the drug of choice.

7. Pneumocystis jirovecii

  • Causes atypical interstitial pneumonia (PCP) in T-cell deficiency (e.g., lymphoma).
  • Symptoms: Dry cough, fever, hypoxia, diffuse infiltrates on X-ray.
  • Diagnosis: Giemsa/Grocott stain, PCR, β-D-glucan positive.
  • Treatment: TMP-SMX; prophylaxis in high-risk patients.

8. Talaromyces marneffei

  • Dimorphic fungus, endemic in Southeast Asia, including Nepal.
  • Disseminated infection in AIDS or hematologic malignancies.
  • Shows red pigment on SDA at 25°C; yeast cells with central septa in tissues.
  • Treated with amphotericin B followed by itraconazole.

Further Readings

  • https://www.dgho.de/arbeitskreise/a-g/agiho/leitlinien/mykosen-antimykotika-therapie-ifd-agiho-ruhnke-rev-mycoses2020-1.pdf
  • https://onlinelibrary.wiley.com/doi/10.1111/myc.13082
  • https://www.sciencedirect.com/science/article/pii/S0924857912000064
  • https://www.cochrane.org/CD000026/GYNAECA_prevention-fungal-infections-patients-cancer-antifungal-drugs
  • https://www.dovepress.com/invasive-candidiasis-in-patients-with-solid-tumors-a-single-center-ret-peer-reviewed-fulltext-article-IJGM
  • https://www.cancernetwork.com/view/management-fungal-and-viral-infections-cancer-patients
  • https://www.artemishospitals.com/blog/black-fungus-mucormycosis-types-causes-symptoms-treatment
  • https://www.dgho.de/arbeitskreise/a-g/agiho/leitlinien/mykosen-antimykotika-therapie-ifd-agiho-ruhnke-rev-mycoses2020-1.pdf
  • https://pmc.ncbi.nlm.nih.gov/articles/PMC7916227/
  • https://www.ncbi.nlm.nih.gov/books/NBK13518/
  • https://www.producer.com/livestock/this-weird-algae-can-cause-severe-infections-in-animals/
  • https://pmc.ncbi.nlm.nih.gov/articles/PMC4047064/
  • https://pmc.ncbi.nlm.nih.gov/articles/PMC6711263/

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