Tumour markers

Question 1

What are some of the characteristics of an ideal tumour marker?

Answer 1

1. diagnostic accuracy
   - Sn: pick up Ca early
   - Sp: test pos for only Ca
2. Staging/prognosis: measure severity
3. Reflects response to therapy and Detects recurrance

Question 2

Using tumour markers to screen the general population for cancers is discouraged. Discuss why

Answer 2

bc for most it doesn’t impact their survival & no affect on overall morality. & having the knowledge of result could be harmful (to know) even though no impact on survival

Question 3

What methods are used for measurement of the tumours markers listed above

Answer 3

Bc tumour markers are present at low [ ], use Sandwich immunoassay w/ highly Sn reporter sys. e.g. Immmunochemiluminometric assay (ICMA)

Question 4

discuss generic methodological issues which may cause interpretive difficulties

Answer 4

Issues:
- Hook effect: High [ ] give low result in sandwich assays
- Heterophilic Aby: give pos & neg. values

Question 5

Give examples of problems that may be encountered with analytical methods for measurement of tumour markers

Answer 5

differences in results b/w assay (diff methods)

Question 6

In assessing the benefit of screening for tumours, why is there an emphasis on survival rather than cancer diagnosis?

Answer 6

bc some tumour markers may not cause harm & affect one’s survival.
bc if it was Ca dx then that would lead to unnecessary treatment causing more harm than benefit e.g. side effects/infections

Question 7

Carcinoembryonic antigen
a) Type of cancer/malignancy of this tumour marker
b) reasons for elevation in non-malignant states

Answer 7

a) Colorectal Ca
- can also be elevated in breast & ovarian malignancies
b) liver disease, inflamm. bowel disease, smoking

Question 8

CA 125
a) Type of cancer/malignancy of this tumour marker
b) reasons for elevation in non-malignant states

Answer 8

a) Ovarian Ca
b) liver disease, preg., mens., pelic inflammation

Question 9

Prostatic specific agent (PSA)
a) Type of cancer/malignancy of this tumour marker
b) reasons for elevation in non-malignant states

Answer 9

a) Prostate Ca
b) benign prostate hypertrophy, UTI, prastatitis, riding a bike, rectal exam.

Question 10

CA19-9: a) Type of cancer/malignancy of this tumour marker
b) reasons for elevation in non-malignant states

Answer 10

a) Pancreatic Ca
- can also be elevated in bowel, lung, gall bladder malignancies
b) cirrhossis, hepatitis, benign breast disease

Question 11

HCG:
a) Type of cancer/malignancy of this tumour marker

Answer 11

a) Trophoblastic tumours
- can also be elevated in germ cell tumours e.g some testicular Ca

Question 12

Type of cancer/malignancy of this tumour marker: alpha Foetoprotein

Answer 12

Liver Ca
- can also be elevated in germ cell tumours

Question 13

Measurment considerations for PSA & other tumour markers

Answer 13

1. Sn methods: good at detecting lo [ ] & recurrance
2. Variable serum half-life: note may need to delay testing if [PSA] is Hi due to pre-analytical error
3. Influence of biological (+/-7%) & analytical variation (+/- 15%)
   *2 & 3 elevations must be confirmed