Pathology: Tumor Identification

Questions and Answers

What percentage of all human cancers does MUO account for?

10-15%

1-2%

20-25%

2-9% (correct)

What is the average age at diagnosis of MUO?

40-50 years

50-60 years

80-90 years

60-75 years (correct)

What is the median overall survival (OS) of patients with MUO?

1-3 months

10-15 months

15-20 months

3-10 months (correct)

What is the most frequently used imaging modality in the management of patients with MUO?

CT Signup and view all the answers

What is included in the diagnostic approach of MUO?

Complete history taking, detailed review of past biopsies or malignancies, and physical examination Signup and view all the answers

What is the primary characteristic of MUO?

Absence of the primary site Signup and view all the answers

What is the purpose of PET/CT scan in MUO?

When radical therapy for local disease is planned Signup and view all the answers

What is the prognosis of patients with MUO?

Poor Signup and view all the answers

What is the histopathological marker for lymphoma?

LCA (LEUCOCYTE COMMON ANTIGEN) Signup and view all the answers

What is the treatment approach for a woman with papillary adenocarcinoma of the peritoneal cavity?

Managed as ovarian cancer Signup and view all the answers

What is the molecular analysis concept for identifying tumor type?

Neoplasm retains gene expression profile based on cellular origin Signup and view all the answers

What is the indication for adjuvant radiation therapy after lymph node dissection?

Disease limited to a single nodal site Signup and view all the answers

What is the histopathological marker for melanoma?

S100, HMB45 Signup and view all the answers

What is the treatment approach for a man with bone metastasis from adenocarcinoma with elevated PSA?

Managed as prostate cancer Signup and view all the answers

What is the principle of radiation therapy for symptomatic patients?

Palliative radiation therapy Signup and view all the answers

What is the histopathological marker for carcinoma?

CK (cytokeratin) Signup and view all the answers

Study Notes

Definition and Epidemiology

MUO (Metastatic Unknown Origin) is a clinical disorder where a patient presents with histologically confirmed metastatic cancer, but standard diagnostic investigations fail to identify the primary site.
Accounts for 2-9% of all human cancers.
Considered to be the 7th-8th most frequent malignant tumor.

Clinical Characteristics at Presentation

Average age at diagnosis of 60 to 75 years.
Heterogeneous tumors with a wide variety of clinical presentations.
Absence of the primary, early dissemination, aggressiveness, and unpredictability of metastatic pattern.
About 80% of patients with MUO have a poor prognosis and median overall survival (OS) of 3 to 10 months.

Major Sites of MUO at Initial Presentation

Lung metastasis
Liver metastasis
Other sites not mentioned

Diagnostic Approach

Complete history taking and detailed review of past biopsies or malignancies.
Physical examination including breast, genitourinary, pelvic, and rectal examinations.
Routine laboratory tests (e.g., complete blood count, electrolytes, liver function tests, creatinine, calcium).
Occult blood stool testing and tumor markers (e.g., CA15-3, PSA).
Imaging:
- Computerized tomography (CT) is the most frequently used imaging modality.
- Magnetic resonance imaging (MRI).
- Breast Ultrasound and MAMOGRAPHY.
- Positron emission tomography (PET) scan and a computed tomography (CT) (PET/CT) for radical therapy planning.
Histopathology:
- Carcinoma (adenocarcinoma, squamous carcinoma): CK (cytokeratin).
- Lymphoma: LCA (LEUCOCYTE COMMON ANTIGEN).
- Melanoma: S100, HMB45.
- Sarcoma: VIMENTINE, S100.
Molecular analysis: Neoplasm retains gene expression profile based on cellular origin.
Endoscopy: Symptoms-guided investigational approach.

Treatment

Favorable Prognosis

Isolated inguinal adenopathy (SCC): Local excision +/- radiotherapy.
Woman with adenocarcinoma involving axillary lymph node: Managed as breast cancer.
Woman with papillary adenocarcinoma of peritoneal cavity: Managed as ovarian cancer.
Adenocarcinoma with colon profile: Managed as colon cancer.
Men with bone metastasis from adenocarcinoma with elevated PSA: Managed as prostate cancer.

Unfavorable Prognosis

Male gender, older age (≥65 years), multiple comorbidities: Treated with empirical chemotherapy ± radiotherapy.
Metastases involving multiple organs (e.g., liver, lung, bone): Treated with empirical chemotherapy ± radiotherapy.
Peritoneal metastases; multiple cerebral metastases; non-papillary malignant ascites (adenocarcinoma): Treated with empirical chemotherapy ± radiotherapy.

Principles of Radiation Therapy

Consider adjuvant radiation therapy after lymph node dissection (if the disease is limited to a single nodal site).
Consider palliative radiotherapy for symptomatic patients with uncontrolled pain, impending pathologic fracture, or impending cord compression.