Neoplasia 3

Question 1

How does a cell get a growth advantage

Answer 1

t begins to secrete a growth factor for which the cell already expresses the receptor (autocrine loop)Platelet Derived GF in glioblastomas (brain cancer).Tumour GFa in sarcomas (cancers of bone/fat/cartilage origin).Fibroblast GF in melanomas.Hepatocyte GF in thyroid tumours.

Question 2

Why do cancer cells not respond to growth inhibitory signals.

Answer 2

he expression of cell cycle inhibitors is disrupted.

Mutation or loss of retinoblastoma.

Mutation or loss of p53.

Mutation or loss of Cdk inhibitors

Question 3

What is the function of the p53 tumour

Answer 3

p53 is a transcription factor that can activate the p21 gene.p21 protein inhibits cyclin/cdk function.Loss of p53 function removes inhibition of cell growth.p53 gene is mutated or deleted in 70% of all cancers.

Question 4

What are the possible defect in apoptosis

Answer 4

Reduction in expression of CD95

Reduced release of cytochrome c from mitochondria due to raised BCL-2 or BCL-XL (anti-apoptotic).

Question 5

What is sustained angiogenesis

Answer 5

Tumours cannot grow to more than 1-2mm without being vascularised.Limit is due to extent of diffusion of oxygen, nutrients and waste through tissues.Therefore cancers must acquire mechanisms to promote new blood vessels (neo-angiogenesis).

Question 6

How does a tumour disseminate

Answer 6

Detachment of tumour cells from neighbouring cells.Degradation of ECM.Attachment to novel ECM components.Migration of tumour cells.