ROBI: Robust and Optimized Biomarker Identifier

ROBI is a selection pipeline that selects predictive biomarkers from any set of features. The selection is performed with a robust and adjustable control of the number of false positives as well as a control for confounders. ROBI can control for confounders and already known biomarkers in order to select only new and relevant information.

Key features:

• 🛡️ Robust control of the number of false positives by passing permuted datasets through the selection pipeline thousands of times. The proportion of false positive can be adjusted.
• ➕ Increased discovery rate via optimised feature selection.
• ⚖️ Reliable predictive power estimation through permutation tests instead of fixed thresholds.
• 🎉 Selects only new information by controlling for confounders and correlations with known biomarkers.
• ⚡ Fast parallelized implementation that can leverage both CPU and GPU for extensive tests: you can easily evaluate tens of thousands of potential biomarkers with millions of permutations in a few minutes.

🚀 Installation

pip install robi

⚡ Although PyTorch is not required to use the package, ROBI runs much faster with its PyTorch implementation. The speed gain is great on CPU, and much greater on GPU. To use the PyTorch implementation, simply install PyTorch (conda is the easiest way), and ROBI will use it automatically. To tell ROBI to use the GPU, set device='cuda' in the robi.make_selection function.

✨ Utilisation

Quick example

Here is an example that you can run if you don't have any data to test ROBI:

import robi
import numpy as np

df, scores = robi.utils.new_synthetic_dataset(n_samples=200,
                                              censoring=0.5,
                                              nb_features=100,
                                              n_informative=10,
                                              effective_rank=None,
                                              noise=0)
res, scores = robi.make_selection(df,
                                  candidates=np.arange(df.shape[1]-2).astype('str'),
                                  targets = {'time': ('time', 'event')})
res

Detailed usage

First, ROBI must be imported:

import robi

Then, a pandas dataframe needs to be defined where each row is a patient, and each column a feature (biomarker, outcome, ...), such as:

print(df)

outcome	candidate_1	candidate_2
10	0	100
25	0.1	-2

with candidate_1 and candidate_2 the candidate biomarkers that we want to evaluate and outcome the target (e.g. the feature that we want to be predicted by the selected biomarkers).

Then, the selection can be performed with:

selection, scores = robi.make_selection(df,
                                        candidates = ['candidate_1', 'candidate_2'],
                                        targets = 'outcome')

robi.make_selection will plot the following image:

The x axis is the degree of permissiveness: how strict is the selection. A low permissiveness means a stricter selection, reducing the number of false positives, but at the cost of more false negatives (e.g. missed discoveries). On the other hand, a high permissiveness means a less strict selection, increasing the number of discoveries but at the cost of more false positives. The orange line represents the number of selected candidates. The blue line represents the average number of false positives. The blue area is the 95% confidence interval for the number of false positives. If the selection is performed on multiple targets, a plot for each target is generated.

robi.make_selection will return two variables:

• selection: contains the results of the selection for multiple level of false discovery rate.
• scores: contains the results of the evaluation of the prognostic value of each candidate.

selection will look like this:

target	permissiveness	n_selected	n_FP	P_only_FP	selected
outcome	0.01	1	0.1 (0-0)	1e-3	['candidate_1']
outcome	0.02	2	0.5 (0-2)	1e-2	['candidate_1', 'candidate_2']
...	...	...	...	...	...

with:

• target: on which target was the selection performed
• permissiveness: degree of permissiveness for this selection
• n_selected: number of selected candidates
• n_FP: average number of false positives and 95% confidence interval in parentheses
• P_only_FP: probability of having only false positives selected
• selected: list of the selected candidates for the corresponding permissiveness

scores will look like this:

candidate	target	C_index	p_value
candidate_1	outcome	0.65	1e-3
candidate_2	outcome	0.55	2e-2
...	...	...	...

with:

• candidate: candidate to whom belong the row
• target: on which target was the C-index computed
• C-index: C-index of the corresponding candidate for the corresponding target
• p-value: p-value of the corresponding C-index

🚨 ⚠️ the C-index is anti-concordant with the targets ⚠️ 🚨

• a feature with a C-index > 0.5 is negatively correlated with the target. The higher the feature value, the lower the target.
• a feature with a C-index < 0.5, is positively correlated with the target. The higher the feature value, the higher the target.

So if the target is the Overall Survival or any other survival metric, a C-index > 0.5 means that the corresponding feature is positively correlated to the risk.

Control for confounders

If confounders are present in the dataset, they can be listed in the confounders parameter. ROBI will discard any candidate that is sensitive to these confounders, making sure that any selected biomarker is relevant and worth studying further.

selection, scores = robi.make_selection(df,
                                        candidates,
                                        targets = 'outcome',
                                        confounders = ['age', 'sex'])

This way, any candidate whose hazard ratio changes by more than 10% when confounders are introduced in a Cox model, will be discarded.

Control for known biomarkers

If some biomarkers are already known and used, we can avoid selecting candidates that are simply replicating this known information. For instance, if we know that tumor volume affect the outcome of patients, we can specify known = ['tumor_volume']such as:

selection, scores = robi.make_selection(df,
                                        candidates,
                                        targets = 'outcome',
                                        known = ['tumor_volume'],
                                        confounders = ['age', 'sex'])

This way, any candidate that is simply a proxy of the tumor volume will be discarded. Multiple known biomarkers can be listed. Collinearity and multicollinearity will be tested.

Censored target

ROBI can handle censored targets (e.g. we know that a patient was alive until a certain date, but then we don't know if he died or when). For instance, to use the Overall Survival (OS), one must specify:

selection, scores = robi.make_selection(df,
                                        candidates,
                                        targets = {
                                            'OS': ('OS_time', 'OS_happened')
                                        })

with OS_time being the time between diagnosis and death or end of study, and OS_happened a boolean feature stating if a patient died (True or 1) or not (False or 0) during the study.

Multiple targets

ROBI can perform the biomarker selection for multiple targets at the same time. For instance, the candidates could be evaluated for OS and Progression Free Survival (PFS). Simply pass them to the targets parameter as a dictionary:

selection, scores = robi.make_selection(df,
                                        candidates,
                                        targets = {
                                            'PFS': ('PFS_time', 'PFS_happened'),
                                            'OS': ('OS_time', 'OS_happened')
                                        })

The key of the dictionary is the name of the target. The first element of the tuple is the time, the second says if the event happened or not.

When giving multiple targets, some could be censored while others might be uncensored. Provide them as shown in the following example:

selection, scores = robi.make_selection(df,
                                        candidates,
                                        targets = {
                                            'uncensored_target': ('uncensored_target'),
                                            'censored_target': ('censored_target_time', 'censored_target_happened')
                                        })

🧑‍💻 Author

Louis Rebaud: louis.rebaud@gmail.com

📄 License

This project is licensed under the Apache License 2.0 - see the LICENSE.md file for details