A researcher is studying the ability of breast cancer cells to metastasize. Neoplastic cells obtained from 30 patients with stage IV ductal carcinoma of the breast are tagged with a fluorescent antibody. The cells are then inserted into a medium resembling normal human tissue. After 2 weeks, all samples show in vitro hematogenous invasion and migration away from the original site of insertion. Which of the following properties is most likely responsible for the ability of these neoplastic cells to metastasize?

Release of matrix metalloproteinase

Presence of fibrous tissue capsule

A 65-year-old man with a 40-pack-year smoking history presents with hemoptysis and a persistent cough. Chest CT shows a 3.5 cm centrally located mass in the right main bronchus. Positron emission tomography confirms a malignant nodule. Bronchoscopy with transbronchial biopsy is performed and a specimen sample of the nodule is sent for frozen section analysis. The tissue sample is most likely to show which of the following tumor types?

Metastasis of colorectal cancer

A 53-year-old farmer presents to the clinic for evaluation of a pigmented lesion on his arm. He states that he first noticed the lesion last year, but he believes that it has been slowly growing in size. He otherwise does not have any complaints and is generally healthy. Which of the following findings on physical exam would suggest a malignant diagnosis?

Different pigmentation throughout the lesion

Flat lesion with symmetric hyperpigmentation

Hyperpigmented lesion with smooth borders

A 26-year-old nulligravid woman presents to her gynecologist after noticing a lump in her right breast while showering. She states that she first noticed the lump approximately 2 weeks ago, when the mass was slightly tender to touch. Since then, the lump has gotten slightly smaller and is now non-tender. The patient is otherwise healthy. She does not take oral contraceptives. Her last menses was approximately 2 weeks ago. There is no family history of cancer. On exam, the patient's temperature is 98.3°F (36.8°C), blood pressure is 116/84 mmHg, pulse is 65/min, and respirations are 12/min. In her right breast, there is a small 1.5 cm mass that is mobile, well-circumscribed, and firm. Which of the following is most likely on histological examination of the mass?

Hypercellular stroma with overgrowth of fibrous and glandular tissues

Large, pleomorphic cells with associated central necrosis and microcalcifications

Cysts with “leaf-like” projections

Terminal duct lobular units surrounded by dense stroma

Dilated glands with 2 cell layers present

A 70-year-old man comes to the physician because of right-sided back pain, red urine, and weight loss for the last 4 months. He has smoked one pack of cigarettes daily for 40 years. A CT scan of the abdomen shows a large right-sided renal mass. Biopsy of the mass shows polygonal clear cells filled with lipids. Which of the following features is necessary to determine the tumor grade in this patient?

Nuclear pleomorphism and nucleolar prominence

Invasion of surrounding structures

Involvement of regional lymph nodes

Size of malignant proliferation

A 62-year-old man seeks evaluation at a local walk-in clinic for mid-low back pain of several weeks. He has tried different rehabilitation therapies and medications with no improvement. He was prescribed some pain medications and sent home last week, but the patient presents today with difficulty walking and worsening of his back pain. He was referred to the ER, where he was examined and found to have hypoesthesia from T12 to S4–S5, significant muscle weakness in both lower limbs, and reduced knee and ankle deep tendon reflexes. A hypotonic anal sphincter with conserved deep anal pressure was demonstrated on digital rectal examination, as well as a multinodular, asymmetric prostate. Imaging studies showed multiple sclerotic bone lesions along the spine. Subsequently, a prostate core biopsy was obtained which confirmed the diagnosis of prostate cancer. Which of the following characteristics would you expect in the specimen?

Well-formed glands with an increase in interglandular stroma

Prostatic intraepithelial neoplasia

Small, closely-packed, well-formed glands

Characteristics of benign vs malignant tumors for USMLE Step 2 CK: High-Yield Pathology Lessons

Benign vs Malignant - The Great Divide

Benign: Well-differentiated, slow-growing, encapsulated, and non-invasive. No metastatic potential.
Malignant: Poorly differentiated (anaplastic), erratic growth, locally invasive, and capable of metastasis.

Feature	Benign	Malignant
Differentiation	Well-differentiated	Poor to anaplastic
Growth Rate	Slow, few mitoses	Rapid, many atypical mitoses
Local Invasion	Cohesive, encapsulated	Infiltrative, non-encapsulated
Metastasis	Absent	Present (definitive sign)

⭐ Anaplasia, the lack of differentiation, is a hallmark of malignancy. However, the most reliable feature distinguishing malignant from benign tumors is metastasis.

Key Characteristics - A Tale of Two Tumors

Feature	Benign Tumors	Malignant Tumors (Cancer)
Differentiation	Well-differentiated; resembles parent tissue.	Poorly differentiated (anaplastic); atypical structure.
Rate of Growth	Slow, progressive expansion; may stop or regress. Mitotic figures are rare.	Rapid, erratic growth; numerous, atypical mitotic figures.
Local Invasion	Cohesive growth; often encapsulated with a fibrous rim. Does not invade surrounding tissue.	Infiltrative growth; invades and destroys adjacent tissues. Poorly demarcated.
Metastasis	Absent.	Frequent; the definitive hallmark of malignancy.

⭐ Anaplasia (lack of differentiation) is the most reliable indicator of malignancy. Key features include pleomorphism (variation in cell size/shape), hyperchromatic nuclei, high nuclear-to-cytoplasmic ratio (N/C ratio), and loss of polarity.

Metastasis - The Great Escape

Metastasis is the single most important feature distinguishing malignant from benign tumors. It is the primary cause of cancer-related death.

Pathways of Spread:
- Seeding of Body Cavities: Peritoneal spread of ovarian cancer.
- Lymphatic Spread: The most common pathway for initial dissemination of carcinomas (e.g., breast cancer).
- Hematogenous Spread: Favored by sarcomas, but also used by carcinomas. Liver and lungs are the most frequently involved secondary sites.
The Metastatic Cascade:

⭐ The sentinel lymph node is the first regional lymph node that receives lymph flow from a primary tumor. Its biopsy is critical for staging and determining treatment for melanoma and breast cancer.

Metastatic cascade: invasion, intravasation, extravasation

High‑Yield Points - ⚡ Biggest Takeaways

Metastasis is the single most reliable feature of malignancy.

Benign tumors are typically well-differentiated, slow-growing, and encapsulated.

Malignant tumors are poorly-differentiated (anaplastic), grow rapidly, and invade local tissues.

Anaplasia implies a loss of structural and functional differentiation in malignant cells.

Malignant cells exhibit pleomorphism, hyperchromatic nuclei, and a high N:C ratio.

Atypical mitotic figures and high mitotic activity are hallmarks of malignancy.

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